the social difficulties inventory (sdi): development of subscales and scoring guidance for staff

Psycho-OncologyPsycho-Oncology 20: 36–43 (2011)Published online 23 February 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/pon.1705

The Social Difficulties Inventory (SDI): developmentof subscales and scoring guidance for staff

Penny Wright1�, Adam B. Smith2, Ada Keding1 and Galina Velikova1

1Psychosocial Oncology and Clinical Practice Research Group, Leeds Institute of Molecular Medicine, University of Leeds, Leeds, West Yorkshire, UK2Centre for Health and Social Care, University of Leeds, Leeds, West Yorkshire, UK

Abstract

Aims: To develop subscales for clinical use of the Social Difficulties Inventory (SDI) with score

interpretation guidance for use in routine oncology practice.

Background: Patient-reported outcome measures are used increasingly in cancer care but

successful implementation is dependent on a combination of sound psychometrics, guidance on

clinical meaning and good clinical judgement. The SDI, a 21-item instrument (SDI-21)

developed for use in cancer care, demonstrated good psychometric properties. Rasch analysis of

the SDI resulted in a 16-item interval scale of Social Distress (SD-16), which allowed for

establishment of some clinical utility guidance but further work was required to optimise

meaningful interpretation in clinical practice.

Data sources: Data were pooled from three studies investigating psychometrics and

clinical utility of the SDI-21.

Statistical analyses: Common factor analysis was undertaken on SD-16 items. Subscales

were derived from the resulting factors and calculated by summing the scores of associated

items. Subscale reliability was evaluated using Cronbach’s a.Results: There were 652 participants. A three-factor model explaining 53.3% of the

variance was extracted forming the basis of the subscales: Everyday living, Money matters and

Self and others. Subscale reliability was good. In a clinical setting, a 2-point change in subscale

score could be interpreted as a clinically meaningful difference.

Conclusion: The development of three subscales and clinically significant difference scores

for the SD-16, combined with the previously developed cut-off points, improves the clinical

utility of the SDI-21 when assessing social issues in oncology care.

Copyright r 2010 John Wiley & Sons, Ltd.

Keywords: cancer; oncology; social difficulties; patient-reported outcomes; clinical utility

Introduction

Patient-reported outcomes (PROs) are being ap-plied in clinical practice for screening and monitor-ing of problems, promotion of patient-centred care,as decision aids, facilitating team communicationand for evaluation of care. However, evidence forefficacy is mixed possibly due to the complexity ofthe intervention which involves not only soundPROs but also training on interpretation of scoresand management guidelines for staff [1]. In theUnited States, guidelines and national initiativeshave been published to promote assessment andmanagement of supportive care needs of cancerpatients including psychological, social and spiri-tual concerns [2]. In 2007 the UK Cancer ReformStrategy [3] included plans for the introduction ofHolistic Common Assessment [4]. The assessmentof psychological, social and spiritual issues wasrequired for all cancer patients at a number ofrecommended time points. For assessment to

become embedded within routine practice, easymethods must be found to allow busy staff toidentify and spend time with patients who areexperiencing problems. Successful implementationentails both psychometrically sound and clinicallymeaningful PROs with trained staff to interpret thescores using guidance provided and clinical judge-ment [5].

Although there is a considerable social impactfollowing a diagnosis and treatment for cancer [6]there are few PROs which include sufficient itemswithin the social domain. As part of a programmeof work aimed at developing and evaluating asystem of routine patient centred assessment, wedeveloped a questionnaire to assess social difficul-ties experienced by cancer patients, the 21-itemSocial Difficulties Inventory (SDI-21) which couldbe used in everyday practice and administeredeither on a touchscreen computer or in paperformat. The National Cancer Action Teamadopted almost in its entirety the items from the

* Correspondence to:Psychosocial Oncology andClinical Practice ResearchGroup, Room SJH.44.L3.141,Level 03, Bexley Wing St.James’s Institute of Oncology,Beckett Street, Leeds LS97TF, West Yorkshire, UK.E-mail:[email protected]

Received: 27 March 2009

Revised: 27 November 2009

Accepted: 28 November 2009

Copyright r 2010 John Wiley & Sons, Ltd.

SDI-21 as part of the assessment guidance for thesocial and occupational domain of Holistic Com-mon Assessment of Supportive and Palliative CareNeeds for Adults with Cancer [4].Each item of the SDI-21 self-report covers a

different area of potential difficulty in daily life:(1) Independence, (2) Domestic Chores, (3) Perso-nal Care, (4) Caring for dependents, (5) Supportavailable for those close to you, (6) Welfarebenefits, (7) Finances, (8) Financial services, (9)Work, (10) Planning the future, (11) Communicat-ing with those close, (12) Communicating withothers, (13) Sexual matters, (14) Plans to have afamily, (15) Body Image, (16) Isolation, (17)Getting around, (18) Where you live, (19) Recrea-tion, (20) Holidays and (21) Other (not specified).The scoring ranges from no difficulty to very muchdifficulty (0–3). For details and examples see theAppendix for the full questionnaire. The first stagesof development of the SDI-21 included reliability,validity and factor structure analyses [7]. Factoranalysis revealed a four-factor structure withfactors labelled: physical ability, providing for thefamily, contact with others and an undefined groupwith no readily definable theme. The SDI-21demonstrated good psychometric properties butas with other instruments this is not sufficient tojustify use with confidence in clinical practice. Inorder to assist the development of a clinicallymeaningful measure of Social Distress based onthe SDI-21, Rasch analysis was undertaken result-ing in a 16-item uni-dimensional interval scale.Disordered categories were observed for four ofthe items, that is the direction of the estimatedid not correspond to the incremental direction ofthe categories. The third and fourth categorieswere therefore collapsed for these items and wererecoded to a 3-category response, i.e. 0,1,2,2. Usingstandard coding and recoding for the disorderedcategories allows summing of the 16 items toproduce a scale of Social Distress (SD-16) [8].In a cross-sectional interview study matchingexpert evaluation with distress scores, a cut-offpoint of X10 on the SD-16 scale was found to bethe optimum indicator of social distress [9]. In a

second study examination of minimally importantdifferences (MIDs) in the SD-16 scale resulted in arecommendation of an estimate of 3 as a clinicallymeaningful difference for use in serial assessment[10]. Table 1 provides an overview of the develop-ment of these measures of social difficulties anddistress.A tool for screening, monitoring or prioritising

problems for use in routine practice must fulfil staffrequirements for brevity, utility, relevance, ease ofuse and simplicity in interpretation [11] withoutcompromising the scope of the tool and evaluationof individual patient-centred issues of concern [12].Accommodating staff demands may result in poorcontent validity. One resolution to this tension isto use a tool with a number of scoring optionsallowing for flexibility according to staff andpatient priorities. Health care professionals nowhave two options for implementing the SDI-21 inroutine patient-centred assessment: use of indi-vidual items for detailed assessment and, for moregeneral assessment, use of the SD-16 scale totalscore with associated scoring guidance. However,when time is short or comparative assessment overtime is required, the means to focus on certainaspects of SD-16 without having to examine eachof the items individually may be beneficial to staff.The aim of this work is to develop subscales fromthe 16-item SD-16 scale with guidance on subscalescore interpretation for use in everyday oncologypractice.

Method

Participants and procedures

Data for this analysis were collated from threeseparate studies: one examining the psychometricproperties [7] and two examining the clinical meaningand utility of the SDI-21 [9,10]. All were approved bylocal ethics research committees. In the psychometricstudy, 270 patients, at different stages of disease,completed the SDI-21 and were then randomised intoeither a test–retest reliability arm or a validation arm.The first study evaluating the clinical meaning and

Table 1. Development of measures of social difficulties and distress

Study Patients Analysis Purpose

[7] Wright et al. (2005) 270 Factor analysis

Test of reliability and validity

Finalise items and explore factor structure

to validate SDI-21

[8] Smith et al. (2007) 609 Rasch analysis Identify meaningful uni-dimensional Social

Distress scale, resulting in SD-16

[9] Wright et al. (2007) 189 Score comparisons between

patients and expert rater

Identify SD-16 cut-off point for caseness

of social distress

ROC Analysis

[10] Wright et al. (2008) 193 Anchor and distribution-based analysis Identify SD-16 clinically meaningful differences

Present study [7]1[9]1[10] 5 652 Factor analysis Develop SD-16 subscales

Distribution-based analysis Identify SD-16 subscale clinically meaningful differences

Copyright r 2010 John Wiley & Sons, Ltd. Psycho-Oncology 20: 36–43 (2011)

DOI: 10.1002/pon

The Social Difficulties Inventory 37

utility of the SDI-21 patients was cross-sectional with189 patients, at different stages of disease, completingthe SDI-21 followed by an interview within a weekof the completion of the questionnaire. In thesecond clinical meaning and utility study, 193 newlydiagnosed patients treated with curative intentcompleted the SDI-21 at baseline and then werefollowed up at 6, 12 and 24 months. Full details ofthese studies are reported in the original publications[7,9,10]. Participants from the three studies wereadult cancer patients recruited from haematology,oncology, chest medicine or surgical wards or out-patient clinics.All participants completed the SDI-21, a number

of other questionnaires and socio-demographicdetails. Clinical data were collected from themedical notes.

Analyses

Factor analysis

Common factor analysis using Principal Axis Factor-ing with the rotational method oblique (Obliminwith Kaiser normalisation) was undertaken on the16 SD-16 items (using standard coding, 12 items,and recoding, 4 items). This was because factorswere expected to be related to each other, followingRasch analysis [13]. Missing data were excludedpair-wise. Factor loadings of less than 0.20 weredisregarded.

Subscales

Scale scores were calculated from SD-16 items byadding together the item scores for each subscale asderived from the factor analysis as well as for thetotal scale of social distress. Internal consistency ofeach summated scale, was evaluated using Cron-bach’s a with a lower acceptable limit of 0.7.

MIDs for subscale scores

In order to interpret the clinical meaning of thederived subscale scores, an analysis of MIDs wasconducted, estimated by 1.0 standard error ofmeasurement (SEM). As a high internal consistencycould be expected from previous studies [5], adistribution-based method was employed to estimateMIDs for the SDI-21 subscale scores. Internalconsistency was evaluated, and the SEM wascalculated for each subscale as a function of thereliability and variance of that scale:SEM ¼ sx

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

1� reliabilityp

. Although MIDs identi-fied in this way will be specific to the socio-demographic and clinical profile of the samplepopulation in this study, they will provide a pointof reference for novel patient groups as well as aframework for developing values for populations ofspecial interest, e.g. young men with germ cell cancer.

Again, internal consistency was consideredacceptable above 0.7 using Cronbach’s a. Bothchanges of 1.0 SEM and the more conservativethreshold of 1.96 SEMs have been shown to be inagreement with MIDs in patient-reported qualityof life measures, 1.0 SEM representing the bestfit [14]. The SEM values denote changes of oneand two standard deviations, respectively, andboth estimates will be included in this study andinterpreted as minimally and moderately clinicallymeaningful differences for each derived subscale.

Results

Participants

Participants were 313 men (median age5 56 yearsand range5 18–88 years) and 339 women (medianage5 56 years and range5 21–88 years). Clinicalcharacteristics are summarised in Table 2.

Analyses

Factor analysis

A three-factor model was extracted explaining53.3% of the variance. The pattern matrix wasreasonably simple with 13 of the 16 SD-16 itemsloading on to one of the three factors only andthree items loading on to more than one factor(Figure 1). Item 10 ‘Planning the future’, loadsalmost equally on to the second factor ‘Moneymatters’ and third factor ‘Self and others’. Item 16‘Isolation’ loads on to two factors but reaches the0.30 level for the third factor ‘Self and others’ only.Item 5 ‘Support available for those close to you’,loads across all three factors and not reaching the0.30 level for any.

Subscales

The pattern matrix was used as the basis for threeproposed subscales. In Figure 1 reliability of the

Table 2. Clinical characteristics of participants (N 5 652)

Characteristic Number (%)

Cancer diagnosis

Breast 132 (20.2)

Gastro-intestinal 107 (16.4)

Haematology 83 (12.7)

Gynaecological 70 (10.7)

Germ cell 60 (9.2)

Head and neck 53 (8.1)

Lung 48 (7.4)

Genito-urinary 45 (6.9)

Other 54 (8.3)

Disease stage

Disease-free survivors 42 years since diagnosis 94 (14.4)

Disease free o2 years since diagnosis 211 (32.4)

Primary local 133 (20.4)

Local recurrent 22 (3.4)

Metastatic 192 (29.4)

38 P. Wright et al.


DOI: 10.1002/pon

three subscales is given for the items grouped asshown. Where items loaded on more than onesubscale (Item 5 ‘Support available for those close

to you’ and Item 10 ‘Planning for the future’), thedecision to keep items within a scale was based onmaintaining the best reliability across the three

Factor 1 Everyday living

1. Independence 0.812. Domestic chores 0.843. Personal care 0.724. Care of dependents 0.4317. Getting around 0.5219. Recreation 0.51

Factor 2Money matters

6. Welfare benefits 0.607. Finances 0.888. Financial services 0.679. Work 0.3910. Planning the future 0.38 (0.36)

Factor 3Self and others

5. Support available for those close toyou (0.29) (0.21) 0.24

11. Communicating with those close 0.7012. Communicating with others 0.8215. Body image 0.4216. Isolation (0.22) 0.36

Eigen values 5.11 1.93 1.47Percentage of variance 31.94 12.11 9.19

Cronbach’s alpha for subscale 0.820 0.743 0.717

Rotation converged in 6 iterations. Factor loadings of less than .20 are not shown. Loadings in brackets denote items not included within the subscale but whose loadings reach the .20 limit and are included in one of the other subscales.

Figure 1. Factor analysis of 16-item Social Distress (SD-16) interval scale

SDI-21 items with SD-16 scoring Subscales Social distress

(SD-16)

Item 1: Independence (0,1, 2,3)I )3,2,1,0(serohccitsemoD:2metI )2,2,1,0(*eraclanosreP:3metItem 4: Care of dependents * (0,1, 2,2)I )3,2,1,0(dnuoragnitteG:71metI )3,2,1,0(noitaerceR:91met

I )3,2,1,0(stifeneberafleW:6metI )3,2,1,0(secnaniF:7metItem 8: Financial services * (0,1, 2,2)I )2,2,1,0(*kroW:9metItem 10: Planning the future (0,1, 2,3)

Item 5: Support available for those close to you (0,1, 2,3)Item 11: Communicating with those close (0,1, 2,3)Item 12: Communicating with others (0,1, 2,3)Item 15: Body image (0,1, 2,3)I )3,2,1,0(noitalosI:61met

*Key emboldened numbers indicate Rasch-adjusted coding

SINGLE ITEMS Item 13: Sexual matters Item 14: Plans to have a family Item 18: Where you live Item 20: HolidaysItem 21: Other

Moneymatters

(range 0–13)

Self and others

(range 0–15)

Soc

ial D

istr

ess

(SD

-16)

(0

-44)

Everyday living

(range 0–16)

Figure 2. Scoring the Social Difficulties Inventory



DOI: 10.1002/pon

subscales. Figure 2 shows the scoring of subscalesbased on the factor analysis.

MIDs for subscale scores

Each of the subscales showed an acceptableinternal consistency ranging between 0.717 and0.820. The calculated SEM values can therefore beconsidered valid distribution-based estimates ofMIDs. Results are summarised in Table 3.All three subscales displayed SEM values of

similar magnitude. Using the more sensitive thres-hold of 1.0 SEM, which will be interpreted as aminimally clinically meaningful difference, achange of score between 1.0 and 1.5 is observed.For the more conservative estimate of 1.96 SEMs,which will be interpreted as a moderately clinicallymeaningful difference, the associated change ofscore is between 2.0 and 3.0. For practical purposesin a clinical setting, a change of about 2 pointscould be considered to represent a meaningfulimprovement or deterioration for an individual oneach of the subscales.

Discussion

Three subscales were identified following factoranalysis of the SD-16 scale with a change in scoreof 2 or more indicating a clinically meaningfulchange in subscale score. Overall guidance on scoreinterpretation now includes a variety of optionsdependent on the type of assessment and timeavailable. The overall SD-16 score provides aquick evaluation of whether or not a patient isbelow or above the cut-off point for SD-16 and, if

assessment is serial the value of change in SD-16and subscale score over time. The subscale scoreswill provide information on the focus of SD-16 andflag when changes in score are of clinical signifi-cance, similar to the ‘nesting’ of the anxiety anddepression subscales within the Hospital Anxietyand Depression scale [15,16]. Thus while the SD-16flags social distress cases, the remaining individualSDI-21 items maintain the content validity of theSocial Difficulties measure. These also allow forchecking and follow-up of associated specific areasof concern to the patient. Recommendations areshown in Figure 3.Graphical output of serial assessment displaying

both SD-16 subscale scores and single-item re-sponses may be of most help to staff. It isanticipated that in the future data will be collectedvia touch screen interfaces, for example, withautomated reporting to clinicians. Clinical staffwould therefore not have to be involved in scoringand summarising responses. In Figure 4 the changein SD-16 and subscale scores with the five singleitems absolute scores are shown for a 61-year-oldwoman with breast cancer who took part in theLongitudinal study [10]. In this case the SD-16score did not reach the cut-off point of 10 at anytime point and therefore would have not triggereddiscussion. However, the change in SD-16 scorebetween baseline and 6 months was a worsening of5 (X3) which would have flagged the need fordiscussion. The subscale contributing most to thiswas Everyday living. Between 6 and 12 months,the SD-16 score did not change and was belowthe cut-off point of 10. If this had been the onlyscore available, no discussion with staff wouldhave been triggered. However, on examination of

Table 3. Descriptive statistics for SD-16 subscales

Scale n Maximum possible score Items Mean SD-16 a 1.00 SEM 1.96 SEM

Everyday living 652 16 6 3.62 3.615 0.820 1.534 3.006

Money matters 652 13 5 1.48 2.346 0.743 1.189 2.331

Self and others 652 15 5 2.09 2.405 0.717 1.279 2.508

Single Assessment

SD-16 Score

Identify and discuss areas of difficulty from subscales

5 single non SD-16 items

Additionally on Follow-Up

≥ 10 High

Scores

SD-16 Change Score

≥ 3

SD-16 Subscale Change Score

≥ 2

Discussion Triggers following SDI-21 administration

Discuss areas of difficulty where scores above threshold

Figure 3. Guidance on SDI-21 score interpretation for use in routine clinical practice

40 P. Wright et al.


DOI: 10.1002/pon

the change in subscale scores it can be seen thatalthough Everyday living improved by a minimalclinically meaningful difference, the Money matterssubscale worsened by a minimal clinically mean-ingful difference, which would have been a promptfor discussion by staff. Using the SD-16 guidanceonly would have masked this change. The singleitems Sexual matters and Holidays may havewarranted some discussion at 6 and 12 months.The Psychometric evaluation of the SDI-21

revealed a four-factor structure explaining 45.8%of the variance [7]. In this analysis two factors ofthe three factors extracted include the same SDI-21items as in the earlier analysis. Differences arefound in the items included in the third factorwhere, in addition to three items in common, twoadditional items (body image, support available forthose close to you) are included. The factoranalysis of the 16 SD-16 items provides a frame-work on which to base the subscales resulting ingood reliability and convincing face validity. Item 5‘Support available for those close to you’ loadedweakly onto all three factors. There may be anargument for discarding this item from anysubscale as loading less than 0.3 may not be con-sidered as meeting minimal criteria for inclusion;however, the Rasch analysis demonstrated clearlythat this item ‘belongs’ with the other 15. This itemreflects different interpretations of support includ-ing practical (Everyday living), financial (Moneymatters) and emotional (Self and others). The

decision to include the item in the ‘Self and others’subscale was taken to increase the reliability of thissubscale. Item10 ‘Planning the future’ loads on totwo subscales almost equally but has been includedin the ‘Money matters’ subscale where loading isgreatest. Discussion with patients should notexclude the possibility that ‘Planning the future’may relate to issues concerning relationships andcommunication. Training for staff using the SDI-21 as part of the Holistic Common Assessmentwould include emphasis on the different interpreta-tions of the items loading on to more than onesubscale and encouragement of staff to explorewith the patient the type of support or planningdifficulties they are reporting.There has been considerable debate over the use

of PROs for use in everyday practice with Garssenand de Kok [17] suggesting that there should be lessfocus on psychometrics, more on clinical utilitywith the main benefit of screening to enhancecommunication and provide systematic care.A recent review identified that screening usingPROs often leads to an increased detection rate ofproblems by clinicians but is rarely followed up byinterventions or associated with an improvement ofpatient symptoms [18]. This may be due to the fit ofthe intervention in clinical practice as well as theattitude of clinicians to the use of quality of lifemeasures for decision making [1].Advantages of using questionnaires to enhance

communication have been demonstrated in two

Serial Assessment SD-16 Overall and Subscales

Cut point

0

2

4

6

8

10

12

14

16

Baseline

Time in months

So

cial

Dis

tres

s S

core

Overall Social Distress

Everyday Living

Money Matters

Self and Others

6 12 18 24

Serial Assessment Non SD-16 Single Items

0

1

2

3

Baseline

Time in months

No

n S

D-1

6 It

ems Sexual Matters

Plans to have a family

Holidays

Where you live

Other

6 12 18 24

Figure 4. An example of graphical output of serial SDI-21 assessment



DOI: 10.1002/pon

randomised studies with nurses [19] and doctors[20]. Recklitis [5] champions the need for goodpsychometrics underpinning screening to avoidmissing those patients whose condition is occultand not coming to clinical attention. Implementa-tion of PROs into routine practice requirespsychometrically sound and clinically useful assess-ment tools, trained staff with good communicationskills and guidance for patient management. Forassessment of the social domain in cancer care,the SDI-21 fulfils the psychometric and clinicalutility requirements. The patients who took part inthese studies represented a wide age range, anumber of cancer sites and patients at differentstages of disease. Older patients and less affluentpatients may be under-represented, as is found inmany research studies. However, in the originalRasch analysis no differential item functioning wasobserved across age groups, gender, stages ofdisease, disease sites and levels of deprivation forthe SD-16, indicating the SD-16 works equally wellfor all groups [8]. Therefore, although there is nocertainty that guidance derived from this samplewill apply to the whole cancer patient population,we believe that we have the basis for reasonablyvalid guidance. A recently completed study willprovide information on a hierarchy of interventionsavailable to staff for support of patients experien-cing social difficulties from simple monitoring toreferral for specialist help. Training for staff onscore interpretation and guidance pathways for

intervention will be developed from this program ofwork resulting in a guidance manual for generaldistribution. Evaluation of the SDI-21 for use inroutine practice will start when the HolisticCommon Assessment is introduced later in the year.

Conclusion

The three SDI-21 subscales with guidance on scoreinterpretation and used in conjunction with theSD-16 cut-off and change score guidance providesan easy method for assessing social issues inoncology care. The development of three subscalesand clinically significant difference scores for theSD-16, combined with the previously developedcut-off points, improves the clinical utility of theSDI-21 when assessing social issues in oncologycare. This should allow health care professionals tofocus on domains of concern using the scores,guidance provided and good clinical judgement.

Acknowledgements

The authors thank the patients who participated in theSocial Difficulties Inventory project and research staff fromthe Psychosocial Oncology and Clinical Practice ResearchGroup. The study was funded by Cancer Research UKgrant number C7775/A7424.

Appendix

42 P. Wright et al.


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DOI: 10.1002/pon

the social difficulties inventory (sdi): development of subscales and scoring guidance for staff

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