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Prejudice Reduction:What Works? A Reviewand Assessment of Researchand PracticeElizabeth Levy Paluck1 and Donald P. Green2

1Harvard Academy for International and Area Studies, Weatherhead Center forInternational Affairs, Harvard University, Cambridge, Massachusetts 02138;email: [email protected] for Social and Policy Studies, Yale University, New Haven,Connecticut 06520-8209; email: [email protected]

Annu. Rev. Psychol. 2009. 60:339–67

The Annual Review of Psychology is online atpsych.annualreviews.org

This article’s doi:10.1146/annurev.psych.60.110707.163607

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0066-4308/09/0110-0339$20.00

Key Words

field experiments, evaluation, stereotype reduction, cooperativelearning, contact hypothesis, peace education, media and readinginterventions, diversity training, cultural competence, multiculturaleducation, antibias education, sensitivity training, cognitive training

AbstractThis article reviews the observational, laboratory, and field experimentalliteratures on interventions for reducing prejudice. Our review placesspecial emphasis on assessing the methodological rigor of existing re-search, calling attention to problems of design and measurement thatthreaten both internal and external validity. Of the hundreds of stud-ies we examine, a small fraction speak convincingly to the questionsof whether, why, and under what conditions a given type of interven-tion works. We conclude that the causal effects of many widespreadprejudice-reduction interventions, such as workplace diversity train-ing and media campaigns, remain unknown. Although some inter-group contact and cooperation interventions appear promising, a muchmore rigorous and broad-ranging empirical assessment of prejudice-reduction strategies is needed to determine what works.

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Prejudice: a negativebias toward a socialcategory of people,with cognitive,affective, andbehavioralcomponents

Contents

INTRODUCTION . . . . . . . . . . . . . . . . . . 340Scope of the Review. . . . . . . . . . . . . . . . 341Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

NONEXPERIMENTAL RESEARCHIN THE FIELD. . . . . . . . . . . . . . . . . . . 343Studies with No Control Group . . . . 343Qualitative Studies . . . . . . . . . . . . . . . . . 344Cross-Sectional Studies . . . . . . . . . . . . 344Quasi-Experimental Panel Studies . . 344Near-Random Assignment . . . . . . . . . 345Conclusion: Nonexperimental

Research . . . . . . . . . . . . . . . . . . . . . . . 345EXPERIMENTAL RESEARCH

CONDUCTED IN THELABORATORY . . . . . . . . . . . . . . . . . . . 345Intergroup Approaches . . . . . . . . . . . . . 345Individual Approaches . . . . . . . . . . . . . . 347Lessons for the Real World from

Laboratory Experiments . . . . . . . . 349Conclusion: Experimental Research

in the Laboratory . . . . . . . . . . . . . . . 351EXPERIMENTAL RESEARCH

CONDUCTED IN THE FIELD. . 351Cooperative Learning . . . . . . . . . . . . . . 352Entertainment . . . . . . . . . . . . . . . . . . . . . 353Discussion and Peer Influence . . . . . . 354Instruction . . . . . . . . . . . . . . . . . . . . . . . . 354Less-Frequently Studied Approaches

in the Field . . . . . . . . . . . . . . . . . . . . . 355Lessons of Field Experimental

Research . . . . . . . . . . . . . . . . . . . . . . . 356Recommendations . . . . . . . . . . . . . . . . . 357

DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . 357Final Thoughts . . . . . . . . . . . . . . . . . . . . 359

INTRODUCTION

By many standards, the psychological literatureon prejudice ranks among the most impres-sive in all of social science. The sheer volumeof scholarship is remarkable, reflecting decadesof active scholarly investigation of the mean-ing, measurement, etiology, and consequencesof prejudice. Few topics have attracted a greater

range of theoretical perspectives. Theorizinghas been accompanied by lively debates aboutthe appropriate way to conceptualize and mea-sure prejudice. The result is a rich array of mea-surement strategies and assessment tools.

The theoretical nuance and methodologi-cal sophistication of the prejudice literature areundeniable. Less clear is the stature of this lit-erature when assessed in terms of the practi-cal knowledge that it has generated. The studyof prejudice attracts special attention becausescholars seek to understand and remedy the so-cial problems associated with prejudice, such asdiscrimination, inequality, and violence. Theiraims are shared by policymakers, who spendbillions of dollars annually on interventionsaimed at prejudice reduction in schools, work-places, neighborhoods, and regions beset by in-tergroup conflict. Given these practical objec-tives, it is natural to ask what has been learnedabout the most effective ways to reduce preju-dice.

This review is not the first to pose this ques-tion. Previous reviews have summarized evi-dence within particular contexts (e.g., the lab-oratory: Wilder 1986; schools: Stephan 1999;cross-nationally: Pedersen et al. 2005), agegroups (e.g., children: Aboud & Levy 2000),or for specific programs or theories (e.g., co-operative learning: Johnson & Johnson 1989;intergroup contact: Pettigrew & Tropp 2006;cultural competence training: Price et al. 2005).Other reviews cover a broad range of prejudice-reduction programs and the theories that un-derlie them (e.g., Oskamp 2000, Stephan &Stephan 2001).

Our review differs from prior reviews inthree respects. First, the scope of our review is asbroad as possible, encompassing both academicand nonacademic research. We augment the lit-erature reviews of Oskamp (2000) and Stephan& Stephan (2001) with hundreds of additionalstudies. Second, our assessment of the preju-dice literature has a decidedly methodologicalfocus. Our aim is not simply to canvass exist-ing hypotheses and findings but to assess theinternal and external validity of the evidence.To what extent have studies established that

340 Paluck · Green


interventions reduce prejudice? To what ex-tent do these findings generalize to other set-tings? Third, building on prior reviews thatpresent methodological assessments of culturalcompetence (Kiselica & Maben 1999) and anti-homophobia (Stevenson 1988) program eval-uations, our methodological assessment pro-vides specific recommendations for enhancingthe practical and theoretical value of prejudicereduction research.

Scope of the Review

We review interventions aimed at reducingprejudice, broadly defined. Our purview in-cludes the reduction of negative attitudes to-ward one group (one academic definition ofprejudice) and also the reduction of relatedphenomena like stereotyping, discrimination,intolerance, and negative emotions toward an-other group. For the sake of simplicity, werefer to all of these phenomena as “preju-dice,” but in our descriptions of individualinterventions we use the same terms as theinvestigator.

By “prejudice reduction,” we mean a causalpathway from some intervention to a reducedlevel of prejudice. Excluded, therefore, are stud-ies that describe individual differences in prej-udice, as these studies do not speak directly tothe efficacy of specific interventions. Our con-cern with causality naturally leads us to placespecial emphasis on studies that use random as-signment to evaluate programs, but our reviewalso encompasses the large literature that usesnonexperimental methods.

Method

Over a five-year period ending in spring 2008,we searched for published and unpublishedreports of interventions conducted with astated intention of reducing prejudice orprejudice-related phenomena. We combedonline databases of research literatures in psy-chology, sociology, education, medicine, policystudies, and organizational behavior, pairingprimary search words “prejudice,” “stereo-

Prejudice reduction:a causal pathway froman intervention (e.g., apeer conversation, amedia program, anorganizational policy, alaw) to a reduced levelof prejudice

type,” “discrimination,” “bias,” “racism,”“homophobia,” “hate,” “tolerance,” “reconcil-iation,” “cultural competence/sensitivity,” and“multicultural” with operative terms like “re-duce,” “program,” “intervention,” “modify,”“education,” “diversity training,” “sensitize,”and “cooperat∗.” To locate unpublished aca-demic work, we posted requests on severalorganizations’ email listservs, including theSociety for Personality and Social Psychologyand the American Evaluation Association, andwe reviewed relevant conference proceedings.Lexis-Nexis and Google were used to locatenonacademic reports by nonprofit groups, gov-ernment and nongovernmental agencies, andconsulting firms that evaluate prejudice. Weexamined catalogues that advertise diversityprograms to see if evaluations were mentionedor cited. Several evaluation consultants sent usmaterial or spoke with us about their evaluationtechniques.

Our search produced an immense databaseof 985 published and unpublished reports writ-ten by academics and nonacademics involvedin research, practice, or both. The assem-bled body of work includes multicultural ed-ucation, antibias instruction more generally,workplace diversity initiatives, dialogue groups,cooperative learning, moral and values edu-cation, intergroup contact, peace education,media interventions, reading interventions, in-tercultural and sensitivity training, cognitivetraining, and a host of miscellaneous techniquesand interventions. The targets of these pro-grams are racism, homophobia, ageism; an-tipathy toward ethnic, religious, national, andfictitious (experimental) groups; prejudice to-ward persons who are overweight, poor, or dis-abled; and attitudes toward diversity, reconcili-ation, and multiculturalism more generally. Weexcluded from our purview programs thataddressed sex-based prejudice (the literaturedealing with beliefs, attitudes, and behaviorstoward women and men in general, as distin-guished from gender-identity prejudices likehomophobia). Sex-based inequality intersectswith and reinforces other group-based preju-dice ( Jackman 1994, Pratto & Walker 2004),

www.annualreviews.org • What Works for Prejudice Reduction? 341


but given the qualitatively different natureand the distinctive theoretical explanationsfor sex-based prejudice and inequality (Eagly& Mlednic 1994, Jackman 1994, Sidanius &Pratto 1999), we believe relevant interven-tions deserve their own review. The resultingdatabase (available at www.betsylevypaluck.com) constitutes the most extensive list of pub-lished and unpublished prejudice-reduction re-ports assembled to date.

This sprawling body of research could beorganized in many different ways. In order tofocus attention on what kinds of valid con-clusions may be drawn from this literature,we divide studies according to research design.This categorization scheme generates threegroups: nonexperimental studies in the field,experimental studies in the laboratory, and ex-perimental studies in the field. SupplementalTable 1 (follow the Supplemental Materiallink from the Annual Reviews home pageat http://www.annualreviews.org) provides adescriptive overview of the database accordingto this scheme. The database comprises 985studies, of which 72% are published. Nearlytwo-thirds of all studies (60%) are nonexper-imental, of which only 227 (38%) use a controlgroup. The preponderance of nonexperimen-tal studies is smaller when we look at publishedwork; nevertheless, 55% of published studiesof prejudice reduction use nonexperimental de-

FIELD VERSUS LABORATORY EXPERIMENTS

In an experimental design, units of observation (e.g., individuals,classrooms) are assigned at random to a treatment and to placeboor no-treatment conditions. Field experiments are randomizedexperiments that test the effects of real-world interventions innaturalistic settings, but the distinction between field and lab isoften unclear. The laboratory can be the site of very realistic in-terventions, and conversely, artificial interventions may be testedin a nonlaboratory setting. When assessing the degree to whichexperiments qualify as field experiments, one must consider fouraspects of the study: (a) participants, (b) the intervention and itstarget, (c) the obtrusiveness of intervention delivery, and (d ) theassessed response to the intervention.

signs. Of the remaining studies, 284 (29%) arelaboratory experiments and 107 (11%) are fieldexperiments (see sidebar Field Versus Labora-tory Experiments). A disproportionate percent-age of field experiments are devoted to school-based interventions (88%).

Within each category, we group studies ac-cording to their theoretical approach or inter-vention technique, assessing findings in lightof the research setting, participants, and out-come measurement. A narrative rather than ameta-analytic review suits this purpose, in theinterest of presenting a richer description of theprejudice-reduction literature. Moreover, themethods, interventions, and dependent vari-ables are so diverse that meta-analysis is poten-tially meaningless (Baumeister & Leary 1997;see also Hafer & Begue 2005), especially giventhat many of the research designs used in thisliterature are prone to bias, rendering theirfindings unsuitable for meta-analysis.

Our review follows the classification struc-ture of our database. We begin with an overviewof nonexperimental prejudice-reduction fieldresearch. This literature illustrates not only thebreadth of prejudice-reduction interventions,but also the methodological deficiencies thatprevent studies from speaking authoritatively tothe question of what causes reductions in preju-dice. Next we turn to prejudice reduction in thescientific laboratory, where well-developed the-ories about prejudice reduction are tested withcarefully controlled experiments. We examinethe theories, intervention conditions, partici-pants, and outcome measures to ask whetherthe findings support reliable causal inferencesabout prejudice reduction in nonlaboratory set-tings. We follow with a review of field exper-iments in order to assess the correspondencebetween these two bodies of research. Becausefield experiments have not previously been thefocus of a research review, we describe thesestudies in detail and argue that field experi-mentation remains a promising but underuti-lized approach. We conclude with a summary ofwhich theoretically driven interventions seemmost promising in light of current evidence,and we provide recommendations for future

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research (see sidebar Public Opinion Researchand Prejudice Reduction).

NONEXPERIMENTAL RESEARCHIN THE FIELD

Random assignment ensures that participantswho are “treated” with a prejudice-reductionintervention have the same expected back-ground traits and levels of exposure to out-side influences as participants in the controlgroup. Outcomes in a randomized experimentare thus explained by a quantifiable combina-tion of the intervention and random chance. Bycontrast, in nonexperimental research the out-comes can be explained by a combination of theintervention, random chance, and unmeasuredpre-existing differences between comparisongroups. So long as researchers remain uncer-tain about the nature and extent of these biases,nonexperimental research eventually ceases tobe informative and experimental methodologybecomes necessary to uncover the unbiased ef-fect (Gerber et al. 2004). For these reasons,randomized experiments are the preferredmethod of evaluation when stakes are high (e.g.,medical interventions).

Prejudice is cited as a cause of health, eco-nomic, and educational disparities (e.g., Amer-ican Psychological Association 2001), as well asterrorism and mass murder (Sternberg 2003).For scientists who understand prejudice as apandemic of the same magnitude as that ofAIDS or cancer, a reliance on nonexperimen-tal methods seems justifiable only as a short-run approach en route to experimental testing.Nevertheless, in schools, communities, organi-zations, government offices, media outlets, andhealth care settings, the overwhelming major-ity of prejudice-reduction interventions (77%,or 367 out of the 474 total field studies in ourdatabase) are evaluated solely with nonexperi-mental methods, when they are evaluated at all.

Studies with No Control Group

The majority of nonexperimental field studiesdo not use a control group to which an inter-

PUBLIC OPINION RESEARCH ANDPREJUDICE REDUCTION

It is ironic but not coincidental that the largest empirical litera-ture on the subject of prejudice—namely, public opinion researchon the subject of race and politics—has little, if any, connectionto the subject of prejudice reduction. Many of the most impor-tant and influential theories about prejudiced beliefs, attitudes,and actions have grown out of public opinion research. Thesetheories examine the role of preadult socialization experiences(Sears 1988), group interests and identities (Bobo 1988), politi-cal culture and ideology (Sniderman & Piazza 1993), and massmedia portrayals of issues and groups (Gilliam & Iyengar 2000,Mendelberg 2001). They diagnose the origins of prejudice, oftentracing it to large-scale social forces such as intergroup compe-tition for status and resources, but rarely do they propose or testinterventions designed to ameliorate prejudice. Taking prejudiceas a fixed personal attribute, this literature instead tends to offersuggestions about how to frame issues (e.g., public spending onwelfare) in ways that mitigate the expression of prejudice (e.g., byreminding respondents that most welfare recipients are white).

vention group may be compared; most eval-uations of sensitivity and cultural-competenceprogramming, mass media campaigns, and di-versity trainings are included in this category.Many no-control evaluations use a postinter-vention feedback questionnaire. For example,Dutch medical students described their expe-riences visiting patients of different ethnici-ties (van Wieringen et al. 2001), and Canadiancitizens reported how much they noticed andliked the “We All Belong” television and news-paper campaign (Environics Research GroupLimited 2001). Other feedback questionnairesask participants to assess their own change:Diversity-training participants graded them-selves on their knowledge about barriers to suc-cess for minorities and the effects of stereotypesand prejudice (Morris et al. 1996). Other no-control group studies use repeated measure-ment before and after the intervention: Wewere unable to locate a sensitivity- or diversity-training program for police that used more thana prepost survey of participating officers. Suchstrategies may reflect a lack of resources for,



Qualitative studies:studies that gathernarrative (textual,nonquantified) dataand typically observerather than manipulatevariables

Cross-sectionalstudy: design inwhich two or morenaturally existing (i.e.,not randomlyassigned) groups areassessed and comparedat a single time point

understanding of, or commitment to rigorousevaluation.

Notwithstanding the frequency with whichthis repeated measures design is used, its defectsare well known and potentially severe (Shadishet al. 2002). Change over time may be due toother events; self-reported change may reflectparticipants’ greater familiarity with the ques-tionnaire or the evaluation goals rather than achange in prejudice. Although such method-ological points may be familiar to the point ofcliche, these basic flaws cast doubt on studies ofa majority of prejudice-reduction interventions,particularly those gauging prejudice reductionin medical, corporate, and law enforcementsettings.

Qualitative Studies

A number of purely qualitative studies haverecorded detailed observations of an interven-tion group over time with no noninterven-tion comparison (e.g., Roberts 2000). Thesestudies are important for generating hypothe-ses and highlighting social psychological pro-cesses involved in program take-up, experience,and change processes, but they cannot reliablydemonstrate the impact of a program. Qualita-tive measurement has no inherent connectionto nonexperimental design, though the two areoften conflated (e.g., Nagda & Zuniga 2003,p. 112). Qualitative investigation can andshould be used to develop research hypothe-ses and to augment experimental measurementof outcomes.

Cross-Sectional Studies

Diversity programs and community desegrega-tion policies are often evaluated with a cross-sectional study. For example, one study re-ported that volunteer participants in a com-pany’s “Valuing Diversity” seminar were moreculturally tolerant and positive about corpo-rate diversity than were “control” employees—those who chose not to attend the seminar(Ellis & Sonnenfield 1994). Even defendersof diversity training would concede that peo-

ple with positive attitudes toward diversity aremore likely to voluntarily attend a diversityseminar. Such evaluations conflate participants’predispositions with program impact. Althoughmany cross-sectional studies report encourag-ing results, post hoc controls for participantpredispositions cannot establish causality, evenwith advanced statistical techniques (Powers &Ellison 1995), due to the threat of un-measured differences between treatment andcontrol groups.

Quasi-Experimental Panel Studies

Prejudice-reduction interventions in educa-tional settings, and some in counseling and di-versity training, are more likely to receive atten-tion from academically trained researchers whoemploy control groups and repeated measure-ment (e.g., Rudman et al. 2001). But with theexception of a few studies that use near-randomassignment, most of these studies’ findings havequestionable internal validity.

For one, many quasi-experimental eval-uations choose comparison groups that aresubstantially different from the interventionparticipants—such as younger students orstudents in a different school. Others choosecomparison groups and assess preinterventiondifferences more exactingly. To evaluate a so-cial justice educational program focused ondialogue and hands-on experience, investiga-tors administered a pretest to all Universityof Michigan freshmen, some of whom had al-ready signed up for the program (Gurin et al.1999). Using this pretest, investigators selecteda control group that was similar to programvolunteers in gender, race/ethnicity, precollegeand college residence, perspective taking, andcomplex thinking. After four years and fourpost-tests, results demonstrated that white stu-dents in the program were, among other things,more disposed to see commonality in inter-ests and values with various groups of colorthan were white control students. This impres-sive study demonstrates the great lengths towhich researchers must go to minimize con-cerns about selection bias, and yet no amount of

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preintervention measurement can guaranteethat the nonrandom treatment and controlgroups are equivalent when subjects self-selectinto the treatment group. Studies such as thisone provide encouraging results that merit fur-ther testing using randomized designs (see alsoRudman et al. 2001).

Near-Random Assignment

Fewer than a dozen studies have used com-parison groups that were composed in anarbitrary, near-random fashion. Near-randomassignment bolsters claims of causal impact in-sofar as exposure to the intervention is unlikelyto be related to any characteristic of the inter-vention group. A good example is a waiting listdesign. In one of the few studies of corporatediversity training able to speak to causal im-pact (Hanover & Cellar 1998), a company’s hu-man resources department took advantage ofa phased-in mandatory training policy and as-signed white managers to diversity training orwaiting list according to company schedulingdemands. After participating in a series of ses-sions involving videos, role-plays, discussions,and anonymous feedback from employees intheir charge, trainees were more likely thanuntrained managers to rate diversity practicesas important and to report that they discour-age prejudiced comments among employees.Unfortunately, all outcomes were self-reported,and managers may have exaggerated the influ-ence of the training as a way to please companyadministration. Putting this important limita-tion aside, this research design represents apromising approach when policy dictates thatall members of the target population must betreated.

Conclusion: NonexperimentalResearch

That we find the nonexperimental literature tobe less informative than others who have re-viewed this literature (e.g., Stephan & Stephan2001) does not mean this research is uninforma-tive with respect to descriptive questions. These

Quasi-experimentalstudies: experimentswith treatment andplacebo orno-treatmentconditions in whichthe units are notrandomly assigned toconditions

Contact hypothesis:under positiveconditions of equalstatus, shared goals,cooperation, andsanction by authority,interaction betweentwo groups should leadto reduced prejudice

studies yield a wealth of information about whatkinds of programs are used with various popula-tions, how they are implemented, which aspectsengage participants, and the like. However, thenonexperimental literature cannot answer thequestion of “what works” to reduce prejudicein these real-world settings. Out of 207 quasi-experimental studies, fewer than twelve can beconsidered strongly suggestive of causal impact(or lack thereof). Unfortunately, the vast ma-jority of real-world interventions—in schools,businesses, communities, hospitals, police sta-tions, and media markets—have been stud-ied with nonexperimental methods. We musttherefore turn to experiments conducted in aca-demic laboratories and in the field to learnabout the causal impact of prejudice reductioninterventions.

EXPERIMENTAL RESEARCHCONDUCTED IN THELABORATORY

Academics studying prejudice reduction in thelaboratory employ random assignment andbase their interventions on theories of prej-udice. Laboratory interventions using inter-group approaches aim at changing group in-teractions and group boundaries. Interventionsusing individual approaches target an individ-ual’s feelings, cognitions, and behaviors. Build-ing on prior reviews (Crisp & Hewstone 2007,Hewstone 2000, Monteith et al. 1994, Wilder1986), we describe an array of laboratory inter-ventions and assess the extent to which thesestudies inform real-world prejudice-reductionefforts.

Intergroup Approaches

Prejudice-reduction strategies that take an in-tergroup approach are based on the general ideathat peoples’ perceptions and behaviors favortheir own groups relative to others. Two majorlines of thought have inspired techniques to ad-dress this in-group/out-group bias: the contacthypothesis (Allport 1954), which recommendsexposure to members of the out-group under



Minimal groupparadigm (MGP):randomly assignedgroups of researchparticipants engage inactivities to observethe power of “merecategorization” on thedevelopment andexpression of in-groupfavoritism, out-groupderogation, and othergroup phenomena

certain optimal conditions, and social identityand categorization theories (Miller & Brewer1986, Tajfel 1970), which recommend inter-ventions that break down or rearrange socialboundaries.

Contact hypothesis. The contact hypothesisstates that under optimal conditions of equalstatus, shared goals, authority sanction, andthe absence of competition, interaction be-tween two groups should lead to reduced preju-dice (Pettigrew & Tropp 2006). Although therehave been dozens of laboratory studies sinceAllport’s original formulation of the hypothesis,among the most compelling are Cook’s (1971,1978) railroad studies. Cook simulated interra-cial workplace contact by hiring racially preju-diced white young adults to work on a railroadcompany management task with two “cowork-ers,” a black and a white research confederate.Participants believed that they were working areal part-time job. Over the course of a month,the two confederates worked with participantsunder the optimal conditions of the contact hy-pothesis. At the end of the study, participantsrated their black coworkers highly in attrac-tiveness, likeability, and competence, a signif-icant finding considering the study took placein 1960s in the American South. Several monthslater, participants also expressed less racial prej-udice than controls expressed in an ostensi-bly unrelated questionnaire about race relationsand race-relevant social policies. This exem-plary piece of laboratory research employed arealistic intervention and tested its effects ex-tensively and unobtrusively.

Social identity and categorization theories.Laboratory interventions guided by social iden-tity and categorization theories address a vari-ety of group prejudices, but often experimenterscreate new groups to study using the well-known minimal group paradigm (MGP; Tajfel1970). Participants are sorted into two groupsbased on an irrelevant characteristic, such asthe tendency to overestimate the number ofdots on a screen (in actuality, assignment to thegroups is random). Simple classification is of-

ten enough to create prejudice between thesenewly formed groups, but some researchers en-hance in-group preference by having partici-pants play group games or read positive infor-mation about their own group. In non-MGPstudies, participants are reminded of a preexist-ing group identity, such as academic or politicalparty affiliation. Once battle lines are drawn,these interventions use one of four kinds ofstrategies for reducing prejudice between thetwo groups: decategorization, recategorization,crossed categorization, and integration—eachof which has generated a subsidiary theoreticalliterature (Crisp & Hewstone 2007).

In a decategorization approach, individ-ual identity is emphasized over group identitythrough instruction or encouragement fromthe researcher. For example, participants inone study were less likely to favor their own(randomly assembled) group over the othergroup when the two groups worked coopera-tively under instructions to focus on individuals(Bettencourt et al. 1992).

In recategorization research, participantsare encouraged to think of people from differ-ent groups as part of one superordinate groupusing cues such as integrated seating, shirts ofthe same color (e.g., Gaertner & Dovidio 2000),or shared prizes (Gaertner et al. 1999). Thesestudies have succeeded in encouraging mem-bers of minimal groups and political affiliation-based groups to favor their in-group less interms of evaluation and rewards and to coop-erate more with the out-group (Gaertner &Dovidio 2000).

Crossed categorization techniques (Crisp &Hewstone 1999) are based on the idea that prej-udice is diminished when people in two op-posing groups become aware that they sharemembership in a third group. Most commonly,prejudice against a novel group is diminishedwhen it is crossed with another novel group cat-egory using the MGP (e.g., Brown & Turner1979, Marcus-Newhall et al. 1993).

Integrative models (Gaertner & Dovidio2000, Hornsey & Hogg 2000b) follow crossedcategorization techniques with their strategyof preserving recognition of group differences

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within a common group identity. In labora-tory experiments, the common group iden-tity is created by highlighting a superordinateidentity (e.g., a university) without diminish-ing the value of identities constituting it (e.g.,science and humanities students; Hornsey &Hogg 2000a) or by having two groups use theirdistinct areas of expertise to solve a task underequal status conditions (Dovidio et al. 1997).

All of these approaches achieve a measureof success in reducing prejudice as defined bypreference for one’s own group. Few labora-tory interventions, especially those that use theMGP, target out-group derogation. The decat-egorization model has been criticized for itsfailure to extend this bias reduction towardthe entire group (Rothbart & John 1985) andfor submerging meaningful subgroup identities(Berry 1984). The integrative and crossed cate-gorization models claim the most empirical andnormative support, and have been used to bol-ster arguments for multicultural policies suchas appreciating ethnic diversity under a com-mon national identity (e.g., Brewer & Gaertner2001, Hornsey & Hogg 2000b). Mixed find-ings from crossed categorization techniquesmay reflect varying definitions of in-group bias(Mullen et al. 2001), or the fact that theseinterventions change the perception of groupboundaries but do not reduce out-group bias(Vescio et al. 2004).

Individual Approaches

Prejudice-reduction techniques aimed at in-dividual phenomena such as feelings andcognitions are guided by a diverse set of the-ories that recommend a wide range of strate-gies, including instruction, expert opinion andnorm information, manipulating accountabil-ity, consciousness-raising, and targeting per-sonal identity, self-worth, or emotion.

Instruction. Ignorance has long been blamedas one of the roots of prejudice (Stephan &Stephan 1984), and the laboratory has beenused to test different instructional solutions.Applied didactic techniques have been devel-

Social norms:perceptions that aredescriptive of whatpeople are doing orprescriptive of whatpeople should do (as amember of a group, anorganization, or asociety)

oped by researchers working with the U.S. mil-itary and with corporations sending employeesoverseas, teaching people how to interpret be-haviors of different cultural and/or racial groups(e.g., Landis et al. 1976).

Other instruction techniques focus on waysto think, such as training in complex think-ing and in statistical logic, with the hypothesisthat this will help individuals avoid faulty groupgeneralizations. These approaches claim mod-est success: After training, students are morelikely to write positive stories about a picturedepicting an interracial encounter, to reportfriendliness toward racial and ethnic out-groups(Gardiner 1972), and to avoid stereotypingfictitious characters presented in a vignette(Schaller et al. 1996).

Expert opinion and norm information. Abody of social psychological research shows thatprejudiced attitudes and behaviors are power-fully influenced by social norms (Crandall &Stangor 2005) and that under certain condi-tions people are persuaded by expert opinion(Kuklinski & Hurley 1996). Telling participantsthat experts believe personality is malleable (aposition that undermines stereotyping; Levyet al. 1998) or that racial stereotyping is not nor-mative for their peer group (Stangor et al. 2001;see also Monteith et al. 1996) reduces stereotyp-ing against stigmatized groups in the laboratory.More subtle manipulations designed to conveya tolerant social norm (e.g., an antiracism ad-vertisement; GR Maio, SE Watt, M Hewstone,& KJ Rees, unpubl. manuscr.) seem to produceweaker effects.

Manipulating accountability. Theories em-phasizing the irrationality of prejudice predictthat asking people to provide concrete rea-sons for their prejudices should reduce them.Accountability interventions have succeededin MGP studies, in which participants allo-cated more points to a fictitious out-groupwhen they were required to justify their alloca-tion amounts (Dobbs & Crano 2001). Studentswho believed they would be held accountableto peers for their evaluations of a Hispanic



Implicit AttitudesTest (IAT): a testinvolving classificationtasks; measuresstrengths of automaticassociations computedfrom performancespeeds

student involved in a school disciplinary casewere also less likely to stereotype this student(Bodenhausen et al. 1994).

Consciousness-raising. Research on im-plicit prejudice proliferated following strikingdemonstrations that prejudiced attitudes andbeliefs can operate without a person’s awarenessor endorsement (Devine 1989). A number of“(un)consciousness-raising” strategies (Banaji2001, p. 136) aim to combat implicit prejudicethrough thought suppression, awareness,reconditioning, and control (see Blair 2002 fora review).

Instructions to suppress stereotypes (i.e.,push them out of awareness) have had the oppo-site intended effect by increasing the accessibil-ity of such stereotypes (Galinsky & Moskowitz2000). For example, business students whowatched diversity training videos instructingthem to suppress negative thoughts about theelderly evaluated older job candidates less fa-vorably than did students who did not receivesuppression instructions (Kulik et al. 2000).Some evidence suggests that stereotype sup-pression does not lead inexorably to higherrates of stereotyping or prejudiced behavior(Monteith et al. 1998), particularly when sup-pression is coupled with mental retraining exer-cises (Kawakami et al. 2000a,b), but the overallpattern of findings suggests suppression is notan effective prejudice-reduction strategy.

Laboratory experiments have also tested theopposite strategy: encouraging awareness ofmemories, attitudes, or beliefs that relate toprejudice. For example, one intervention re-quired students to remember a time when theytreated an Asian person in a prejudiced man-ner (Son Hing et al. 2002). As predicted, stu-dents who previously scored high on an implicitprejudice test—by solving word fragments withthe negative stereotypical Asian words “sly” and“short”—were more likely to feel guilt overthis memory and to encourage funding foran Asian student association on a subsequentquestionnaire.

Other laboratory interventions aim to re-condition implicit attitudes and beliefs. Some

use classical conditioning techniques—pairingstigmatized groups with positive images andwords—to improve college students’ implicitstereotypes about the elderly, black Ameri-cans, and skinheads (Karpinski & Hilton 2001;Kawakami et al. 2000a,b; Olson & Fazio 2008).Presenting positive images of famous blackpeople (e.g., Martin Luther King) and neg-ative images of famous whites (e.g., CharlesManson) reduced implicit prejudice as mea-sured by the Implicit Attitudes Test (IAT;Greenwald et al. 1998), but conscious attitudesremained unchanged (Dasgupta & Greenwald2001, Wittenbrink et al. 2001). Other stud-ies alter implicit attitudes and social dis-tancing behaviors through approach-avoidanceconditioning—i.e., by asking subjects to pullforward on a joystick when presented withwords or faces representing a stigmatized group(Kawakami et al. 2007).

Targeting emotions. Psychologists contendthat emotional states can influence the expres-sions of prejudice (e.g., E. Smith 1993), andsome perspective-taking interventions encour-age the perceiver to experience the target’s emo-tions (Batson 1991). Writing an essay from theperspective of an elderly person decreased sub-sequent stereotypes about the elderly; writingan essay from the perspective of the oppo-site MGP group led to more positive ratingsof the out-group’s personality characteristics(Galinsky & Moskowitz 2000, Vescio et al.2003). Instructions to be empathic whenreading about everyday discrimination againstblacks eliminated the difference betweenparticipants’ evaluations of white and blackAmericans (Stephan & Finlay 1999). Simi-larly, instructions to “focus on your feelings” asopposed to thoughts when watching a videoportraying anti-black discrimination increaseddesire to interact with blacks, an effect thatwas explained by a change in emotions to-ward blacks as a group (Esses & Dovidio 2002).This particular intervention did not changeparticipants’ beliefs or policy endorsementsconcerning blacks.

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Targeting value consistency and self-worth.Two related social psychological theories ofmotivation explain how the need to maintainconsistency among valued cognitions or be-haviors or to protect their self-worth mightmove people to express or repress prejudice.Festinger’s cognitive dissonance theory (1957)has been used in several laboratory interven-tions that encourage participants to see preju-dice as inconsistent with some valued attitudeor trait. For example, college students were alsomore likely to soften pre-existing anti-black po-sitions on social policies and to report moreegalitarian attitudes and beliefs after agreeingto write public statements in favor of pro-blackpolicies (Eisenstadt et al. 2003).

Steele’s self-affirmation theory (1998) pre-dicts that people will resist derogating otherswhen their own self-worth is affirmed. Labo-ratory results are supportive: Individuals whoaffirmed their self-image by writing about theirvalues or who received positive feedback abouttheir intelligence were more likely to rate aJewish job candidate positively in terms of herpersonality and her suitability for the job (Fein& Spencer 1997). Receiving positive feedbackfrom a black manager of the laboratory exper-iment also decreased the amount of negativeblack stereotypes on a word-completion task(Sinclair & Kunda 1999).

Lessons for the Real World fromLaboratory Experiments

Laboratory experiments test a wide range ofprejudice reduction theories with a high degreeof creativity and precision. Computers, videocameras, and even physiological measurementstrack manifestations of prejudice change. Thelaboratory environment and the experimentalmethod lead to tight, internally valid conclu-sions about the causal impact of the interven-tion.

But do laboratory experiments yield reliablestrategies for prejudice reduction in the world?Specifically, in the drive for simplification andabstraction, do laboratory experiments elimi-nate elements of their interventions, environ-

Self-affirmationtheory: predicts thatwhen the self is underthreat, people derogateothers to affirm theirself-identity; theyrefrain from other-derogation when theiridentity is affirmed

ments, and theories that are critical to the exter-nal validity of their lessons for real-world prej-udice reduction?

Interventions. Laboratory studies typicallytest quick fixes. Consider a typical minimalgroup paradigm experiment, in which preju-dice is created, modified, and reassessed overthe course of one hour. Brief manipulations canhave powerful effects (e.g., Bargh et al. 1996),but studies rarely test to see if the change lastslonger than the study period.

Many laboratory prejudice interventionsare also subtle; above we reviewed techniquesbased on slight changes in instructions, t-shirtcolor, and seating assignments. By contrast,real-world institutions are much more heavy-handed: They impose speech codes, citizenshiprequirements, immigration quotas, and eco-nomic sanctions that shape intergroup percep-tions and relationships. Lessons on the powerof authority and conformity handed down byMilgram, Asch, and Zimbardo have notbeen fully exploited in laboratory prejudice-reduction research. Two exceptions areresearch on conformity to perceived normsof prejudice (e.g., Stangor et al. 2001) and onorders to suppress stereotyping (e.g., Galinsky& Moskowitz 2000). Subtle manipulationsundoubtedly have many advantages and ap-plications, yet an exclusive focus on subtletechniques means that the laboratory is notapproximating the full range of situationalinterventions.

A broader point is that laboratory interven-tions are often separated and abstracted fromtheir real-world modalities. For example, in lab-oratory studies of empathy and prejudice reduc-tion, participants receive instructions from theexperimenter to imagine others’ feelings. In theworld, this message would be evoked within amoving speech, by a movie, or by the exam-ple of a peer. People interpret messages differ-ently depending on who delivers the messageand in what manner (Kuklinski & Hurley 1996).Laboratory studies eliminate larger institutionsand social processes in which interventions areembedded—which may fundamentally change



the impact and intervening psychological pro-cesses of the intervention.

Environment. Laboratory experiments them-selves supply evidence challenging the exter-nal validity of the laboratory environment—toname a few, the presence of others affects emo-tional reactions (Ruiz-Belda et al. 2003), and abrief discussion with a peer can eliminate theinfluence of an authority’s opinion (Druckman& Nelson 2003). The lack of correspondencebetween mundane living conditions and labo-ratory environments may be particularly damn-ing for prejudice research, given some theoret-ical views that prejudice is a social norm set bypeers and by the structure of the immediatesituation (Crandall & Stangor 2005). Labora-tory experiments like Cook’s railroad job exper-iments address this concern by making the lab-oratory both an experimentally controlled anda realistic environment.

Populations. Warnings that North Americancollege students differ from the general popu-lation (Sears 1986) are often acknowledged butdisregarded by laboratory researchers. Thesestudents, who comprise the overwhelming ma-jority of laboratory participants, are particularlyexceptional when it comes to expressions ofprejudice. At least in the United States, collegestudents report less prejudice than does the av-erage individual ( Judd et al. 1995) and are moreaware of social proscriptions against the expres-sion of prejudice (Crandall et al. 2002). Collegesubjects come to the lab having had more expo-sure to some form of diversity or antibias train-ing (McCauley et al. 2000).

Prejudices. If prejudice were likened to a sick-ness, many laboratory interventions would bewalk-in clinics, built to handle low-grade prej-udices. Many studies get around the problemof college students’ politically correct responsepatterns by studying socially acceptable preju-dices against skinheads, political parties, or theelderly (e.g., Karpinski & Hilton 2001). More-over, prejudices created with the minimal groupparadigm for maximum experimental control

lack the historical, political, and economicforces that animate and sustain real-world prej-udice, and “. . .a fundamental challenge remainsto discover ways of changing ‘hard-core’ preju-diced beliefs” (Monteith et al. 1994).

Outcome measures. Measuring prejudice is aformidable challenge for all types of research,including laboratory studies. Behaviors mea-sured in the laboratory are often low-stakes ab-stractions of real-world behaviors, such as giv-ing up tokens to another group or brief interac-tions with a stranger. Laboratory investigatorsalso rely on indirect measures to measure racialand ethnic prejudice. The linguistic bias indexis an indirect measure in which verbs and nounsfrom participants’ writing samples are classifiedaccording to their implication that out-groupfailings are dispositional while in-group failingsare situation-specific (Maass 1999). Other mea-sures gauge subtle forms of unease or reticencemore than antipathy. One example is “immedi-acy behaviors,” such as physical posture towardand distance from another person (Kawakamiet al. 2007).

Controversy surrounds the interpretation ofa “prejudiced score” on tests of implicit prej-udice such as the IAT. Some studies find im-plicit prejudice to be correlated with the disin-tegration of real-world interracial friendships(Towles-Schwen & Fazio 2006), but a recentmeta-analysis found that across 32 studies theIAT’s ability to predict discriminatory behaviorvaries widely and sometimes inexplicably (AGGreenwald, TA Poehlman, E Uhlmann, & MRBanaji, unpubl. manuscr.). Other measures ofimplicit prejudice, such as word fragment com-pletion (e.g., “short” versus “smart” in the caseof Asians; Son Hing et al. 2002), are not em-pirically linked to behavior. Most importantly,few studies have connected the reduction of im-plicit prejudice with a reduction in prejudicedbehavior.

Theories. A thorough review of theories de-veloped in the laboratory goes beyond thescope of this essay, but we note that theory de-velopment in the laboratory mostly takes its

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lead from other laboratory experiments. Weworry this creates a theoretical echo chamber inwhich ideas are not cross-fertilized by researchconducted in real-world settings. Additionally,most theory developed in laboratories addressesone or two dimensions of prejudice, (e.g., cog-nition and behavior); one may question whetherthese theories are sufficiently multifaceted topredict how and when prejudice is expressedor changed in real-world settings (Paluck2008).

The ultimate arbiters of the debate about theexternal validity of prejudice-reduction labora-tory studies are research programs that strad-dle the two settings. Currently, such programsare extremely rare. An exception is the coopera-tive learning research program (e.g., Johnson &Johnson 1989, Roseth et al. 2008), in which fieldstudies are sometimes inconsistent with labora-tory results (e.g., Rich et al. 1995). One researchprogram hardly settles the issue, and the corre-spondence between findings in the lab and fieldmerits active investigation.

Conclusion: Experimental Researchin the Laboratory

Reviewers of the psychological prejudice-reduction literature regularly comment that“. . . promising laboratory studies always needto be tested in field settings” (Miller &Harrington 1990, p. 218), but translation israrely attempted, and psychologists frequentlyoffer their laboratory findings as guidance forpolicymakers (e.g., Crisp & Hewstone 2007,p. 239). Those interested in creating effec-tive prejudice-reduction programs must remainskeptical of the recommendations of labora-tory experiments until they are supported byresearch of the same degree of rigor outside ofthe laboratory.

EXPERIMENTAL RESEARCHCONDUCTED IN THE FIELD

Over a half-century ago, psychologist StuartCook endeavored to make his research “. . . bothsocially useful and scientifically meaningful”

(Selltiz & Cook 1948) by using lab and sur-vey methods to develop the theoretical mod-els he then tested using “true experiments” inthe field (Cook 1985, p. 452). To what extenthave prejudice-reduction researchers followedthis example?

Of the hundreds of reports culled from ourliterature search, we identified 107 randomizedfield experiments. Thirty-six of these were stud-ies of cooperative learning, which means that 71experiments speak to the efficacy of all othertypes of prejudice interventions. To put thisnumber into perspective, a PsychInfo databasesearch for studies of one type of prejudice—implicit—retrieves 116 empirical articles. Ourreview’s database contains four times as manylaboratory experiments and five times as manynonexperimental field studies as noncooper-ative learning field experiments; this groupof 71 studies is further dwarfed by the hun-dreds and perhaps thousands of unevaluated an-tiprejudice interventions implemented yearly inschools, businesses, and governments. Becausethe cooperative learning experiments have beensummarized elsewhere (Roseth et al. 2008),Supplemental Table 1 is confined to the 71remaining studies.

Supplemental Table 1 describes these 71field experiments, from the earliest in 1958 topresent. Eighty percent of the studies are fromNorth America. Almost one-third of these stud-ies address prejudice against African Ameri-cans, 20% address multiple prejudices or aremore generally “antibias” treatments; 13% ofthe studies address a non-African Americangroup prejudice, including Mexican and Na-tive Americans; 11% of the studies address“cultural competence”—comfort and ability tointeract with people of different cultures. Ofthe remaining 18% of studies, 6 address prej-udice against the disabled, 3 address preju-dices against immigrants or refugees, 3 addressreligious prejudice, and 1 addresses prejudiceagainst gay men.

Fifty-six percent of the interventions lastedone day or less. Excluding the coopera-tive learning studies, 84% of interventionstudies took place with students or school



personnel. This means antiprejudice educationhas developed a research literature, whereas therest of the prejudice-reduction enterprise lacksrandomized controlled evaluations.

Evaluations also focus on volunteers (e.g.,Haring 1987, Pagtolun-an & Clair 1986,Stewart et al. 2003). It is easy to understandwhy, for practical reasons, interventions wouldtend to be directed toward people who are opento their messages. Unfortunately, field researchon prejudice reduction does not have much tosay about influencing those who do not signup for antiprejudice interventions. Four stud-ies took place in settings of extreme intergroupconflict, measuring reactions to peace educa-tion, a media program, and diversity trainingin Israel, Rwanda, and South Africa, respec-tively. The literature provides little empiricalguidance to policymakers seeking to intervenewith populations living in conflict or postcon-flict environments.

The breadth of answers to the question“What reduces prejudice in the world?” nar-rows further when we probe these studies’designs. Several suffer from weak outcomemeasurement. Most rely solely on self-reportquestionnaires; only 11 studies involve directlyobserved measures of behavior (two gatherthird-party reports). We would expect be-havioral measurement to be the strength offield studies, which take place in environmentswhere the behaviors of interest actually oc-cur. Many clever unobtrusive measures of real-world behavior have been developed (Crosbyet al. 1980), but these measurement techniquesare rarely used in this literature. One of the fewexceptions is a study of a disability awarenessprogram that used audit study methods, send-ing disabled and nondisabled confederates toask for help from employees who had attendedthe program (Wikfors 1998).

Inadequate power is another frequent prob-lem; approximately half of the studies havesample sizes of below 100 individuals. Thir-teen of the studies with larger sample sizes as-sign groups (e.g., classrooms, schools) to treat-ment and control groups but fail to make thenecessary corrections for intracluster correla-

tions within groups when calculating signifi-cance levels.

We now review the best of prejudice-reduction interventions and theories testedwith field experiments. The most frequentlystudied interventions are cooperative learning(34% of all field experiments), entertainment(reading and media: 28%), discussion and peerinfluence (16%), and instruction (15%). Wealso review interventions that receive a greatdeal of attention in the lab but seldom in fieldsettings: contact (10% of field experimentalstudies), cognitive training (5%), value consis-tency and self-worth interventions (4%), andsocial categorization (2%).

Cooperative Learning

Derived from Deutsch’s (1949) theory of so-cial interdependence and best known throughEliot Aronson’s “Jigsaw classroom” technique(Aronson et al. 1978), cooperative learninglessons are engineered so that students mustteach and learn from one another. For exam-ple, teachers in Jigsaw classrooms give each stu-dent one piece of the lesson plan, so that goodlesson comprehension requires students to puttogether the pieces of the “puzzle” collectively.Approximately eight variants on this basic co-operative learning model exist (Slavin et al.1984). Expected outcomes include interper-sonal attraction, perspective taking, social sup-port, and constructive management of conflict.

Meta-analyses of the effects of cooperativetechniques (which included nonexperimentalresults) on relationships crossing ethnic, racial,and ability boundaries have consistently con-firmed a positive impact of cooperation onoutcomes such as positive peer relationshipsand helpfulness ( Johnson & Johnson 1989,Roseth et al. 2008). The few studies that in-vestigate generalization of cross-group friend-ships to individuals outside of the immedi-ate classroom find weaker effects (cf., Warringet al. 1985). Fewer studies measure general-ization to the entire racial or ethnic group ortrack long-term effects. Nevertheless, the co-operative learning literature sets the standard

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for programmatic field research on causalmechanisms. That 79% of all U.S. elementaryschools by the early 1990s used cooperativelearning (Puma et al. 1993) attests to the influ-ence a well-documented causal effect can haveon policy implementation.

Entertainment

Books, radio, television, and film are vivid andpopular couriers of many kinds of social and po-litical messages. Uncle Tom’s Cabin, published byHarriet Beecher Stowe in 1852, was heraldedas the turning point in American abolitionistopinion—not only for the information it pro-vided about the brutality of slavery, but also forits ability to “go to the heart” (cited in Strange2002, p. 263).

Reading and media interventions, most ofthem using an engaging narrative rather than aninformational style, comprise 42% of all non-cooperative learning prejudice-reduction fieldexperiments. We analyze the reading interven-tions separately because they share the specificmodality of a book, but all of these interventionspotentially draw from many of the same changeprocesses via narrative persuasion or extendedcontact, which we describe below.

Reading. All 17 field experiments on the im-pact of reading on prejudice were conductedin schools—studies have yet to examine theeffect of literature on prejudice among gen-eral audiences. One clear advantage of thesereading experiments is that they evaluate sub-stantially longer interventions compared toother field interventions. Whereas half of allfield experiments focused on an interventionlasting one day or less, reading interventionslasted five weeks on average. Children in pre-Kthrough high school were randomly assignedto read stories from or about other cultures(Gwinn 1998; Wham et al. 1996) about African,Native American, or disabled people (Clunies-Ross & O’Meara 1989, Fisher 1968, Hughes2007, Yawkey 1973), or about contact betweenchildren from different groups (Cameron &Rutland 2006, Cameron et al. 2006, Liebkind& McAlister 1999, Slone et al. 2000).

Eleven of the 17 field experiments on read-ing report positive results, mostly for self-reported attitudinal outcomes; none measuredbehavior. The evidence is mixed or null formulticultural literature, more positive for por-trayals of people of another culture or race,and wholly positive for books that portray con-tact between children who are similar to theaudience and children of different cultures orraces. For example, Cameron & Rutland (2006)randomly assigned 253 five- to eleven-year-oldEnglish schoolchildren to listen to stories abouta nondisabled child’s close friendship with adisabled child. The books described the twochildren’s adventures, such as exploring in thewoods. Across the three randomized condi-tions, the books emphasized characters’ indi-vidual characteristics versus their group mem-bership, versus a different unrelated story. Likeeight other reading field experiments, this in-tervention included a group discussion ledby the experimenter at the end of the story.Story hours took place once per week for sixweeks.

The positive attitudinal effects found in thisstudy and in four others that examined sto-ries about intergroup friendship are consistentwith the positive impact of vicarious experi-ences of cross-group friendship that is predictedby the extended contact hypothesis (Wrightet al. 1997). Theories of narrative persuasionsuggest additional processes that could explainprejudice reduction findings from reading fieldexperiments that were not as theoretically mo-tivated. For example, stories are channels forcommunicating social norms—descriptions ofwhat peers are doing (and therefore what thereader or listener should do; Bandura 1986,2006). Narratives encourage perspective taking(Strange 2002) and empathy (Zillmann 1991);texts can “transport” us into an imaginativeworld where we inhabit other characters, learnnew things, and in general remove filters thatmight otherwise screen out different perspec-tives (Gerrig 1993, Green & Brock 2002).

Media. We found 13 media studies, 7 of whichwere one-time viewing experiences, such as a



documentary or an educational movie. Becausefew programs were based on theory, it is dif-ficult to draw broad lessons from the patternof their findings, but like many of the readingstudies, their results are suggestive for those in-terested in narrative persuasion, empathy, per-spective taking, social norms, and the like. Mostmedia experiments were conducted in schools,on media-driven multicultural or antibias edu-cation. Few have gauged the impact of mediaon large audiences or the impact of large-scalemedia campaigns (which span long periods oftime or multiple theatres, cable networks, orairwaves). Two exceptions are a study of a chil-dren’s multicultural television series (Mays etal. 1973) and of a “reconciliation” radio soapopera.

A year-long field experiment in Rwanda(Paluck 2008, Paluck & Green 2008) testedthe impact of a radio soap opera featuring afictional story of two Rwandan communitiesand their struggles with prejudice and violence.The program aimed to change beliefs usingdidactic messages and to influence perceivednorms through realistic radio characters whocould speak to audience experiences. Nearly600 Rwandan citizens, prisoners, and genocidesurvivors listened to the program or to a healthradio soap opera. The investigators found theradio program affected listeners’ perceptions ofsocial norms and their behaviors with respect tointermarriage, open dissent, cooperation, andtrauma healing, but did little to change listen-ers’ personal beliefs. The program also encour-aged greater empathy. The results pointed to anintegrated model of behavioral prejudice reduc-tion in which intergroup behaviors are linkedmore closely to social norms than to personalbeliefs.

Discussion is featured in many studies ofentertainment, because storytelling and me-dia consumption are inherently social practices,and also because an implicit theory in much in-tervention design is that peer discussion ampli-fies message impact. We now turn to considerdiscussion and peer influence as interventionsin their own right and how they have fared infield experimental research.

Discussion and Peer Influence

Although psychologists examine group discus-sion for processes related to polarization of at-titudes and minority influence, they seldom fo-cus on communication for prejudice reduction.One of the few exceptions is Fisher (1968),which found that the addition of discussionstrengthened the positive attitudinal effects ofa reading intervention.

Evidence of the benefits (and potentialpitfalls) of discussing opinions about inter-group relations is also found in peer influ-ence studies. For example, Blanchard and col-leagues (1991, 1994) find that white universityfemales’ opinions about a racial incident oncampus conformed to the publicly expressedopinions of confederates who were randomlyassigned to condone, condemn, or remain neu-tral in their reactions. Another study of norms, afield experiment assessing the Anti-DefamationLeague Peer Training program (Paluck 2006b),showed that students were able to influenceclose friends and casual acquaintances in theirschool with public behaviors such as speakingout against biased jokes. Although few fieldexperiments have experimentally isolated theeffects of normative communication and dis-cussion in field interventions of prejudice re-duction, these findings indicate that theories ofsocial norms and mechanisms of small groupor peer discussion are promising avenues forresearch and intervention.

Instruction

Under the umbrella category of “instruction”we find myriad interventions: multicultural ed-ucation, “ethnic studies,” stand-alone lectures,awareness workshops, and peace education.Few instructional techniques are guided by the-oretical models of learning or prejudice reduc-tion (see Bigler 1999 critiquing multiculturaleducation in particular). The lack of theory mayexplain in part the lack of impressive findings.One notable exception is Lustig’s (2003) inves-tigation of a peace education program in Israelthat aimed to increase perspective taking and

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empathy using instruction about foreign con-flicts. Twelfth-grade Israeli Jewish studentswere randomly assigned to a “permanentpeace” curriculum (versus no curriculum) aboutconflicts in ancient Greece and modern-dayIreland. Questionnaire-based opinions aboutthe Israeli-Palestinian conflict revealed no ef-fect of the curriculum, but there were strikingdifferences between essays students were askedto write from the Palestinian point of view.Curriculum student essays were more likelyto be written in the first as opposed to thethird person, and they were more sympatheticto damages and to the symmetry of Israeli-Palestinian conflict. This study is an excellentexample of the benefits of multiple and non-traditional outcome measurement, and of in-terventions informed by theories of prejudicereduction.

Less-Frequently Studied Approachesin the Field

Given the academic focus on the contact hy-pothesis, social identity theory and related so-cial categorization strategies, cognitive forms ofprejudice, and motivational theories of identityand dissonance, the field experimental litera-ture on these areas is surprisingly thin.

Contact hypothesis. What is most notableabout field experiments categorized as “con-tact” experiments is their general lack of re-semblance to the conditions of contact speci-fied by Allport (1954). Within the small body offield experiments on contact, there is also a ten-dency to address prejudices that may be morerelated to unfamiliarity (e.g., disability) than toantipathy.

Among more recent studies, we find two ofnote. One study capitalized on random assign-ment of minority and white students to collegedorm rooms (Duncan et al. 2003). The exper-iment’s findings from a subsequent Internet-based survey are important for their suggestionthat cross-race contact affects more general at-titudes such as support for affirmative action, al-though weak effects on other attitudinal and be-

Social identity andcategorizationtheory: describes howsocial groupclassification producesperceptions ofmultiple, crossed, andhierarchically arrangedsocial identities, andhow group identitiesgive rise to phenomenasuch as in-groupfavoritism andout-group derogation

havioral outcomes suggest this finding requiresmore study. The second study, conducted withthe Outward Bound camping expedition orga-nization, randomly assigned 54 white teenagersto racially homogeneous (all white) or hetero-geneous expedition groups (Green & Wong2008). In these expeditions, an experiencedleader teaches campers group survival tech-niques under most of Allport’s (1954) condi-tions for ideal intergroup contact: equal status,a common (survival) goal, authority sanction,and intimate contact. One month after the two-to three-week trip, in an ostensibly unrelatedphone survey, white teens from the heteroge-neous groups reported significantly less aver-sion to blacks and gays and described them-selves as less “prejudiced” compared to the ho-mogeneous group teens. The intensity and nat-uralistic quality of the intervention recall theseminal field study of contact, the Sherif et al.(1961) Robbers Cave experiment. The study’slimitations—small sample size, the lack of be-havioral outcome measures, and short-termfollow-up—invite replication and extension.

Social identity and categorization. Althoughprinciples of social identity and categorizationtheory broadly inform some field interventions(e.g., Cameron & Rutland 2006), very few fieldexperiments have been designed to test crossed,integrated, re- and decategorization strategiesdeveloped in the laboratory. Two exceptions arestudies by Nier et al. (2001) and Houlette et al.(2004) testing the Common Ingroup Identitymodel.

Over the course of 12 hour-long sessions,instructors in 61 randomly assigned first- andsecond-grade classrooms led discussions aboutsex, race, and body size exclusion from the“green circle of community” (Houlette et al.2004), versus an enhanced program, versusno program. In the enhanced program, theperimeter of the classroom was circled withgreen tape and all students wore the same greenvests. Mixed, modest results showed that chil-dren in the program classrooms were slightlymore likely to favor drawings of cross-sexor -race children. Weight remained a powerful



predictor of children’s hypothetical choices ofplaymates. The enhanced program did not am-plify these effects (which speaks to our previousquestion about the real-world effects of sub-tle laboratory interventions such as seating ar-rangements and similar clothing).

Value consistency and self-worth. Com-pared to their importance in the laboratoryliterature, studies of the motivating forces ofconsistency and self-worth are scarce in thefield experimental literature. A notable excep-tion is the Rokeach value confrontation tech-nique (Gray & Ashmore 1975, Rokeach 1971).Rokeach (1971, 1973) lectured college studentsabout (fictitious) research findings on valuesrevealing people who value equality are morelikely to be sympathetic toward black Ameri-cans’ civil rights (during this historical period,most North American students favored equal-ity but not black civil rights). In postinterven-tion questionnaires that stretched as far as 17months later, students from the lecture and theno-lecture classes increased their support ofblack civil rights, perhaps in part through expo-sure to the more liberal college atmosphere, buttreatment students eventually outpaced othersin their support (Rokeach never corrected forintraclass correlations, which should lead tomore caution about the statistical significanceof his findings). Twenty-one months later, twiceas many experimental as control subjects wereenrolled in an ethnic core course, and three tofive months after the intervention, 51 treatmentversus 18 control participants responded to so-licitations sent by the NAACP (although a com-parable number of control students respondedthe following year). Although the strength ofthese results is at times mixed, this series ofstudies is notable for its behavioral measuresand longitudinal design.

Cognitive training. Excellent laboratory andquasi-field experimental research has exam-ined stereotype retraining with young children(Levy 1999, Levy et al. 2004), but there arevery few studies of cognitive retraining in thefield experimental literature. Five field experi-

ments, all conducted on North American stu-dents, show weak results in both the short- andlong-term (e.g., Katz 1978, 2000).

Lessons of Field ExperimentalResearch

The strongest conclusion to be drawn fromthe field experimental literature on prejudicereduction concerns the dearth of evidence formost prejudice-reduction programs. Few pro-grams originating in scientific laboratories,nonprofit or educational organizations, gov-ernment bureaus, and consulting firms havebeen evaluated rigorously. Theories with thestrongest support from the laboratory some-times receive scant attention in the field. Entiregenres of prejudice-reduction interventions,including moral education, organizational di-versity training, advertising, and cultural com-petence in the health and law enforcement pro-fessions, have never been tested, as well ascountless individual programs within the broadgenre of educational interventions.

Nonetheless, the field experimental liter-ature on prejudice reduction suggests sometentative conclusions and promising avenuesfor reducing prejudice. Cooperative learningemerges as an important tool for breaking downboundaries between students. This researchprogram should be emulated and extended.More research is needed on the behavioral andlongitudinal impact of cooperative learning andits impact on out-group dislike as well as in-group preference.

Media and reading interventions bear outassorted predictions of the extended contacthypothesis and of narrative persuasion, specif-ically that extended contact can reduce out-group hostility, and narratives can communi-cate norms and inspire empathy and perspec-tive taking. Theoretically driven programs ofresearch on entertainment and narrative inter-ventions would systematize what is at present arather disjointed set of studies and findings. Ex-tended contact and narrative persuasion mightalso provide frameworks for other strategiesassociated with empathy or perspective taking

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such as role playing (e.g., the Jane Elliot BlueEyes/Brown Eyes intervention; Stewart et al.2003), which have met with mixed success,perhaps in part because of a lack of theoreti-cal grounding.

Given the importance of social psychologi-cal processes such as obedience and conformity,experimental evaluations of peer influence anddiscussion should become a priority for futurefield research. Isolating the influence of discus-sion from the impact of the intervention itselfis an important future step (Kelman & Fisher2003, p. 335).

Recommendations

Few rigorous field studies to date have ad-dressed psychology’s most important theoriesof interpersonal and intrapersonal prejudicechange: contact, social identity and categoriza-tion, identity and value-motivated techniques,and social cognitive (stereotype and implicitprejudice) interventions. We recommend morefield experimentation on social psychology’sprincipal theories of prejudice.

The strength of field experimentation restsnot only in its ability to assess causal relation-ships but also in its ability to assess whetheran intervention’s effects emerge and endureamong the cacophony of real-world influencesincluding larger political and economic changesand proximal social pressures and distractions.We recommend that more field experimentsassess the strength and persistence of effectswith outcome measurement that moves beyondthe site of the intervention. Types of outcomemeasures should be increased to capture preju-dice from different angles, especially with un-obtrusive and behavioral measures, and the set-tings should be expanded so as to augment ourknowledge about changing prejudice outside ofthe classroom and with older populations.

Although laboratory studies concentrate oninterventions targeted at specific forms of prej-udice (e.g., stereotyping), the complexities ofreal-world contexts often force the field exper-imentalist to design and parse the impact ofmultidimensional interventions aimed at sev-

eral forms of prejudiced speech, behavior, andattitudes. Studying prejudice reduction in thefield opens our eyes to the utility of more mul-tidimensional theories of prejudice reduction.Field experimentation can be productive for as-sessing the functional interdependence of cog-nitive, affective, normative, and other formsof prejudice, and thus for building prejudice-reduction theories based on this recognition ofthe interrelationships and on the sequencingand long-term effects of change in one part ofthe system (e.g., an intervention that changessocial norms, which then affect behaviors andfinally beliefs; see Paluck 2008 for one suchattempt). Field experimentation is not only amethod for testing theoretical ideas developedin the laboratory—the field itself should be usedas a laboratory for generating richer, more mul-tidimensioned theory.

DISCUSSION

In terms of size, breadth, and vitality, the prej-udice literature has few rivals. Thousands ofresearchers from an array of disciplines haveaddressed the meaning, measurement, and ex-pression of prejudice. The result is a literatureteeming with ideas about the causes of prej-udice. In quantitative terms, the literature onprejudice reduction is vast, but a survey of thisliterature reveals a paucity of research that sup-ports internally valid inferences and externallyvalid generalization.

In order to formulate policies about how toreduce prejudice, one currently must extrapo-late well beyond the data, using theoretical pre-suppositions to fill in the empirical blanks. Onecan argue that diversity training workshops suc-ceed because they break down stereotypes andencourage empathy. Alternatively, one can ar-gue that such workshops reinforce stereotypesand elicit reactance among the most prejudicedparticipants. Neither of these conflicting argu-ments is backed by the type of evidence thatwould convince a skeptic. We currently do notknow whether a wide range of programs andpolicies tend to work on average, and we arequite far from having an empirically grounded



Table 1 Summary of prejudice-reduction approaches, theories, and future directions for research

Intervention approach Theoretical frameworks Evidence neededSupported by experimental evidence from field and laboratoryCooperative learning Social Interdependence Theory Longitudinal, generalization to wider groups,

reduction of negative out-group attitudesEntertainment Extended contact, narrative persuasion

(empathy, perspective taking, transport-imagery), social norm theory, social cognitivetheory

Theory-driven programmatic research; studies oflonger duration and with adults

Peer influence,discussion/dialogue

Social norm theory, small group influence,social impact theory, contact hypothesis

Field experimental evidence; isolation of effects ofdiscussion from other aspects of intervention

Contact Contact and extended contact hypothesis Field experimental evidence for differing contactconditions and more antagonistic groups

Value consistency andself-worth

Cognitive dissonance, self-affirmation andself-perception theory

Field experimental evidence; evidence with“unmotivated” populations

Cross-cultural/interculturaltraining

Acculturation theory, Bhawuk/Landis model Field experimental evidence; behavioral,longitudinal effects

Supported mostly by laboratory evidenceSocial categorization Social identity theory, crossed-categorization,

common in-group identity, de- andrecategorization

Field experimental evidence; evidence withantagonistic groups and longitudinal effects

Cognitive training Implicit prejudice, classical conditioning Field experimental evidence; longitudinal effectsIn need of theoretical and research supportDiversity training Dependent on technique/modality used Theory-driven intervention design and field

experimentationMulticultural, antibias, moraleducation

Socialization theories of prejudice, cognitive,moral development and learning theories

Field experimental evaluations with longitudinaloutcome measurement

Sensitivity, culturalcompetence for health andlaw

Dependent on technique/modality used Theory-driven intervention design and fieldexperimentation

Conflict resolution Interactive conflict resolution models Theory-driven field experimentation

understanding of the conditions under whichthese programs work best.

Looking across all of the settings, popula-tions, and methodologies used to study the re-duction of prejudice, we classify the main ap-proaches to prejudice reduction according tothe evidence accumulated thus far for their im-pact in the real world, and we list theories andmethods that could point the way forward (seeTable 1).

Cooperative learning is the most outstand-ing example of theoretically driven, program-matic laboratory and field research; we hopefuture research will address questions aboutthe longevity and generality of cooperativelearning’s effects. Although media, reading, and

other forms of narrative and normative commu-nication are not currently considered cutting-edge approaches, we point to the apparent suc-cess of this technique in the real world andto its potential for reducing prejudice throughnarrative persuasion, social norms, empathy,perspective taking, and extended contact. Thepersuasive and positive influence of peers (indi-rectly via observation or directly via discussion)is a promising area of prejudice reduction sup-ported by laboratory research (Stangor et al.2001) and by creative real-world interventions(Aboud & Doyle 1996; Blanchard et al. 1991,1994; McAlister et al. 2000; Nagda et al. 2004;Paluck 2006b) highlighting the communicativeand normative nature of prejudice change.

358 Paluck · Green


The contact hypothesis, which benefitedfrom early and innovative field and laboratorystudies, remains unproven in the real worlddue to the limited number of randomized stud-ies conducted in field settings and the narrowrange of prejudices tested in those studies. Re-searchers should aspire to extend real-world ex-perimental tests to domains such as summercamps, multinational peacekeeping units, andrefugee settlements. Other approaches that re-quire more field experimental tests are con-sistency and self-worth interventions based onbalance and self-affirmation theories, as wellas cross-cultural training approaches. Giventhat motivation is a critical lever of change forthese interventions, field tests would illuminatewhether these techniques are successful withparticipants who are unmotivated to change,and what adjustments are needed in order toreach this population. Interventions aimed atchanging cognitions (e.g., stereotypes or auto-matic associations) or cognitive abilities (e.g.,complex thinking or statistical reasoning) havesuccessfully reduced prejudice in the laboratory,but the magnitude and persistence of these ef-fects also await testing in real-world settings.

Several areas of prejudice reduction are inneed of research and theory. Although antibias,multicultural, and moral education are popu-lar approaches, they have not been examinedwith a great deal of rigor, and many applica-tions are theoretically ungrounded. Spendingon corporate diversity training in the UnitedStates alone costs an estimated $8 billion annu-ally (cited in Hansen 2003), and yet the impactof diversity training remains largely unknown(Paluck 2006a). Despite research showing thatmedical practitioners’ negative bias can affecttheir administration of care (Flores et al. 2000)and reports of sharply increased demand withinthe law enforcement field following September2001 (New York Times, Jan. 23, 2005), sensitiv-ity trainings administered to medical personneland police are rarely based on theory or sub-jected to rigorous evaluation. Finally, althoughthere is a distinguished tradition of psycholog-ical research on conflict resolution for elite ne-gotiators (Kelman & Fisher 2003), there is lit-

tle sustained experimental evaluation of conflictnegotiation and reduction for the many millionsof ordinary citizens living in conflict or postcon-flict settings (G Salomon & B Nevo, unpubl.manuscr.; cf., Bargal & Bar 1992).

Final Thoughts

Field experiments present a range of practi-cal challenges, but we believe that the failureto implement field experimental designs is inpart a failure of creativity. Random assignmentto waiting lists solves the problem of controlgroups who wish to undergo treatment and rep-resents a low-cost opportunity for randomizedfield experimentation. Randomly phasing in aprogram to different parts of a target populationsolves the problem of the “saturation model” in-tervention. For interventions where it is abso-lutely impossible to leave out a control group,researchers can use rigorous and underappre-ciated quasi-experimental techniques such asregression discontinuity (Shadish et al. 2002).A lack of field experimental training amongpractitioners who evaluate prejudice-reductionprograms, doubts about the feasibility of ran-domized field methodology, and insufficient in-centives for academics to conduct “applied”research all contribute to the scarcity of ran-domized field experiments in prejudice reduc-tion. We believe that each of these limitationscan be overcome through partnerships betweenacademics and practitioners (which is how wehave conducted our prejudice-reduction workto date; e.g., Green & Wong 2008; Paluck2006b, 2008; Paluck & Green 2008).

Laboratory research plays an important rolein the process of developing and testing in-terventions, but too often this process stopsshort of real-world tests. The result is a dearthof rigorously tested interventions and also ofrigorously tested theoretical ideas. We urgemore research programs in the spirit of psy-chologists such as Stuart Cook, Kurt Lewin,and Donald Campbell: hypothesis generationthrough field observation, and interventiontesting with parallel laboratory and field ex-periments. The imperative to test ideas in the



field will keep theories appropriately complexand attuned to real-world conditions, and con-tinually revisiting the laboratory will help torefine understandings of the causal mecha-nisms at work, which in turn helps inspire newinterventions.

In addition to becoming more methodologi-cally rigorous, the study of prejudice reductionmust branch out substantively. As our reviewof the literature demonstrates, the kinds of in-terventions that have been evaluated do not pitprejudice against its strongest potential adver-saries. Studies to date have largely relied on pas-sive and indirect interventions such as coopera-

tive contact. What if interventions were insteadto harness forces such as obedience and confor-mity, the very forces that have been implicatedin some of the most notorious expressions ofprejudice in world history? If people can be in-duced to express prejudice at the behest of po-litical leaders, can they also be induced to repu-diate prejudice if instructed to do so? If socialcues induce conformity to prejudiced norms,can social cues also induce conformity to toler-ant norms? The prejudice-reduction literatureshould be regarded as an opportunity to assessthe power and generality of basic psychologicaltheory.

SUMMARY POINTS

1. Notwithstanding the enormous literature on prejudice, psychologists are a long wayfrom demonstrating the most effective ways to reduce prejudice. Due to weaknessesin the internal and external validity of existing research, the literature does not revealwhether, when, and why interventions reduce prejudice in the world.

2. Entire genres of prejudice-reduction interventions, including diversity training, educa-tional programs, and sensitivity training in health and law enforcement professions, havenever been evaluated with experimental methods.

3. Nonexperimental research in the field has yielded information about prejudice-reductionprogram implementation, but it cannot answer the question of what works to reduceprejudice in these real-world settings.

4. Laboratory experiments test a wide range of prejudice-reduction theories and mecha-nisms with precision. However, researchers should remain skeptical of recommendationsbased upon environments, interventions, participants, and theories created in laboratorysettings until they are supported by research of the same degree of rigor outside of thelaboratory.

5. Laboratory research and field research are rarely coordinated; in particular, manyprejudice-reduction theories with the strongest support from the laboratory receive scantattention in the field.

6. Field experimentation remains a promising but underutilized approach. Promising av-enues for prejudice reduction based on existing field experimentation include cooperativelearning, media, and reading interventions.

FUTURE ISSUES

1. More field experimentation can provide evidence that is missing, particularly for thecontact hypothesis, peer influence and discussion/dialogue interventions, values and self-worth interventions, social categorization theory, and cognitive training.

360 Paluck · Green


2. Theoretical perspectives and more rigorous evaluation methods should be brought tobear on common prejudice interventions such as diversity training; multicultural, antibias,and moral education; sensitivity and cultural competence training; and conflict resolution.

3. Psychologists should look to historical exemplars of theoretically and methodologicallyrigorous applied prejudice-reduction studies, such as those conducted by Stuart Cook.The hallmark of Cook’s work was theoretically grounded randomized field interventionsand highly realistic experimental laboratory interventions.

4. In addition to becoming more methodologically rigorous, the study of prejudice reduc-tion must branch out substantively to include more direct interventions based on classicpsychological findings (e.g., those that leverage the power of conformity and authority).Researchers should also strive to reduce deeply held prejudices rather than the moretransitory prejudices associated with “minimal” groups.

DISCLOSURE STATEMENT

The authors are not aware of any biases that might be perceived as affecting the objectivity of thisreview.

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Readers can find the database of studies included in this review (full citation, abstract, and method-ological categorization) posted at www.betsylevypaluck.com. On the same Web site, we haveposted an alternative version of this review that includes more historical references and studydetails.


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