Lecture Outline Introduction to experimental research

Introduction to correlational research

Three types of research validity

Class Activity

Experimental ResearchOverview and Major Features

An independent variable (IV) is manipulated A dependent variable(s) (DV) is measured Many basic experiments consist of two levels of the

independent variable experimental group control group

Control over extraneous variables holding constant randomizing effects

A causal relationship between the independent and dependent variables can be established

Basic Goal of Experimental Design Manipulate possible values of the IV

Observe behavioral changes as indexed by values of the DV

Basic Characteristics of Experimental Designs

Subjects are randomly assigned to research groups

A given participant must be equally likely to be assigned to any of the given groups

Random number table Flip a coin

In experimental designs, a causal relationship between the independent and dependent variables can be established

Independent Variable

Differing values of the IV are called “levels” May vary quantitatively

10 mg day 20 mg day

e.g. here are 2 levels of variable dosage

May vary qualitatively Zoloft Imipramine Prozac

e.g. here are 3 levels of the variable medication type

•An operational definition is a clearly defined set of procedures for measuring or manipulating the construct of interest.

•The key to an acceptable operational definition is that the procedure is specified precisely enough to allow replication by others.

Examples:quality of memory -- accuracy of recall in a certain taskdepression -- Beck Depression Inventory (survey) scorearousal -- galvanic skin response (conductivity of the surface of the skin)

Operational Definitions

She is a good carsalesperson

She:1. Sells many cars2. Points out + features3. Is nice4. Sells only good cars

Verbal StatementVerbal Statement Operational DefinitionOperational Definition

Operational Definitions: Examples

Stress

1. Environment/Number of stressors a. Number negative Life events b. Number of Examinations2. Self-report Measurable Nervous mood3. Behavior a. number of fidgets/minute b. Psychophysiological responses elevated

Verbal StatementVerbal Statement Operational DefinitionOperational Definition

Operational Definitions: Examples

Identify Key Experimental Features Social loafing refers to people’s tendency to slack

on group tasks. In one study on social loafing college participants cheered alone, and in groups of 2, 4, or 6 ppl. They were told to cheer as loud as possible at specific times so researchers could determine how much noise people made in social settings. The amount of noise made by each participant dropped as group size increased.

1) What is the IV? 2) What is the DV? 3) Why is random assignment important here?

Correlational Research: Major Features

No independent variables are manipulated

Two or more variables are measured and a relationship established

Correlational research does not show causality

Don’t confuse statistics with research design Correlation coefficients ( a statistic) can be used in correlational or

experimental research designs (although they are more commonly used in correlational designs)

Correlational Research

2 Variables

Positive and Linear Negative and Linear

Example of Non-Linear RelationshipYerkes-Dodson Law

Performance

Arousal

BetterBetter

WorseWorse

LowLowHighHigh

Correlation Does Not Imply Causation

Causality – must demonstrate that changes in one variable can only be due to influence of the other variable

Directionality of Effect Problem

Third Variable Problem

Directionality of Effect Problem

XX YY

XX YY

XX YY

XX YY

XX YY

Class Class AttendanceAttendance

Higher Higher GradesGrades

Class Class AttendanceAttendance

Higher Higher GradesGrades

Directionality of Effect Problem

XX YY

XX YY

Aggressive BehaviorAggressive Behavior Viewing Violent TVViewing Violent TV

Aggressive BehaviorAggressive Behavior Viewing Violent TVViewing Violent TV

Aggressive children may prefer violent programs orViolent programs may promote aggressive behavior

Directionality of Effect Problem

Third Variable Problem

XX YY

ZZ

Class ExerciseIdentify the

third variable

that influences both X and Y

Third Variable Problem

Number ofNumber ofChurchesChurches

CrimeCrimeRateRate

++

Third Variable Problem

ClassClassAttendanceAttendance

GPAGPA++

Third Variable Problem

Ice CreamIce CreamConsumedConsumed

Number ofNumber ofDrowningsDrownings

++

Measurement Considerations Variables should be measured accurately

and consistently.

Accuracy Validity

Bathroom scale gives correct weight

Consistency Reliability

Bathroom scale gives same weight consistently

Evaluating Research: 3 Validities Validity

How accurate is the information from our research?

Three validities Construct validity Internal validity External validity

Construct Validity

Construct Validity The degree to which the construct can be inferred from

the operational definition of that construct Never one perfect operationalization

Schacter and Singer (1962) Two-factor theory of emotion:

Emotions require arousal and label Factor 1: AROUSAL

Participants received epinephrine shots and either informed them of side-effects or not

Factor 2: LABEL Participants around "euphoric" or "angry“ confederate

How Valid are These Manipulations? Euphoria

Confederate shoots rubber bands, plays with hula hoops and crumples up paper and practices hook shots into wastebasket

Anger Confederate complains about the injection, adds

negative comments about the questionnaire they are filing out and ends up ripping up the questionnaire.

Simplified Results

Euphoria Euphoria ConditionCondition

Anger Anger ConditioConditio

nn

Informed of epinephrine effects

Uninformed of epinephrine effects

Internal and External Validity Internal validity

The extent to which the observed effect is caused only by the experimental treatment condition

The ability to draw conclusions about a causal relationship from our data

Experiments usually high in this External validity

The extent to which the results can be applied to and across different persons, settings and times

AKA generalizability Experiments often low in this

Generalizing From the Lab Setting Mundane realism

The extent to which an experiment is similar to real-life situations

Psychological realism The extent to which an experiment triggers relevant

psychological and group processes Key point

Lab experiments not automatically artificial When an experiment lacks mundane realism it may be

very realistic in terms of psychological realism

Assess Internal & External Validity

Does lighting affect productivity?

Study 1: Give people a production task in a

laboratory. The lab room is either bright or dim. Measure and compare their productivity (how quickly and accurately they perform the task).

Study 2: Give employees in a well-lit office and those

in a dim office a production task. Measure and compare their productivity (how quickly and accurately they perform the task).

The Tradeoff Real life situations

High external validity Hard to rule out other explanations

Low internal validity

Lab settings High internal validity Often artificial and findings can’t be

generalized Low external validity

Class Exercise

Hypothesis and Operational Definition Exercise