Chapter 5Chapter 5Measuring VariablesMeasuring Variables

From Hypothesis to DesignFrom Hypothesis to Design One of the first steps in designing an One of the first steps in designing an

experiment is to operationally define experiment is to operationally define the variables.the variables.– IV – The causal variableIV – The causal variable

There must be at least two different levels of There must be at least two different levels of the independent variable.the independent variable.

– Presence (experimental treatment) vs. Presence (experimental treatment) vs. absence (control condition), or can have multiple absence (control condition), or can have multiple levelslevels

– The differences are in AMOUNT or TYPEThe differences are in AMOUNT or TYPE

– Control Variables – Those that need to be Control Variables – Those that need to be held constant across levels of the IVheld constant across levels of the IV

– DV – The effect/outcome variableDV – The effect/outcome variable

Operational DefinitionOperational Definition

An explicit definition in terms that can be An explicit definition in terms that can be used to operate the research designused to operate the research design

Operational definitions allow other Operational definitions allow other researchers to replicate research exactly.researchers to replicate research exactly.

Operational definitions can be found by Operational definitions can be found by searching the literature.searching the literature.

For a dependent variable, the operational For a dependent variable, the operational definition is a precise description of how definition is a precise description of how it is it is measuredmeasured..

Ways of asking questionsWays of asking questions

Fixed alternative questionsFixed alternative questions– Questions where the respondent selects his Questions where the respondent selects his

or her answer from a set of specified or her answer from a set of specified responses.responses.

Open-ended questionsOpen-ended questions– Allows the respondent to provide his or her Allows the respondent to provide his or her

answer in his or her own words.answer in his or her own words.– Often summarized with content analysis.Often summarized with content analysis.

Rating ScalesRating Scales– Fixed alternative questions where the Fixed alternative questions where the

respondent indicates magnitude on a scale.respondent indicates magnitude on a scale.

Ways of asking questionsWays of asking questions

Likert ScalesLikert Scales– Statements in which the respondent is Statements in which the respondent is

asked to indicate the degree he or she asked to indicate the degree he or she agrees or disagrees with the statement.agrees or disagrees with the statement.

Semantic DifferentialSemantic Differential– The respondent rates words on a series The respondent rates words on a series

of bipolar scales.of bipolar scales.– Designed to measure the psychological Designed to measure the psychological

distance between the connotative distance between the connotative meanings of words.meanings of words.

ExampleExample

Alcohol and AggressionAlcohol and Aggression– Social Information Processing StudiesSocial Information Processing Studies

Free ResponseFree Response– What do we do with the answers?What do we do with the answers?– ValidityValidity

Item RatingItem Rating– How does this map onto behavior?How does this map onto behavior?

Social desirability Social desirability and response setand response set

Socially desirable respondingSocially desirable responding – – giving giving answers that respondents think are answers that respondents think are appropriate or that they think the appropriate or that they think the researchers might want to hearresearchers might want to hear

Response setResponse set – – giving only moderate giving only moderate answers or always agreeing or disagreeing.answers or always agreeing or disagreeing.

You can deal with these problems by:You can deal with these problems by:– Altering the wording on some items.Altering the wording on some items.– Stressing anonymity.Stressing anonymity.– Including irrelevant items.Including irrelevant items.

Before voting I thoroughly investigate the Before voting I thoroughly investigate the qualifications of all the candidates.qualifications of all the candidates.

I never hesitate to go out of my way to help someone I never hesitate to go out of my way to help someone in trouble.in trouble.

It is sometimes hard for me to go on with my work if I It is sometimes hard for me to go on with my work if I am not encouraged.am not encouraged.

I have never intensely disliked someone.I have never intensely disliked someone. On occasion I have had doubts about my ability to On occasion I have had doubts about my ability to

succeed in life.succeed in life. I sometimes feel resentful when I don’t get my way.I sometimes feel resentful when I don’t get my way. I am always careful about my manner of dress.I am always careful about my manner of dress. My table manners at home are as good as when I eat My table manners at home are as good as when I eat

out in a restaurant.out in a restaurant. If I could get into a movie without paying and be sure I If I could get into a movie without paying and be sure I

was not seen, I would probably do it.was not seen, I would probably do it. On a few occasions, I have given up doing something On a few occasions, I have given up doing something

because I thought too little of my ability.because I thought too little of my ability.

Measuring observed Measuring observed behaviorbehavior

Typical ways that psychologists Typical ways that psychologists measure observable behavior:measure observable behavior:– AccuracyAccuracy – responses are either right or – responses are either right or

wrong.wrong.– FrequencyFrequency – how often a behavior occurs in – how often a behavior occurs in

a specified period of time.a specified period of time.– LatencyLatency – speed of onset. – speed of onset.– DurationDuration – how long the behavior lasts. – how long the behavior lasts.– AmplitudeAmplitude – size of response. – size of response.– Choice selectionChoice selection – frequency of choice – frequency of choice

between alternatives.between alternatives.

ExampleExample Alcohol and Aggression StudyAlcohol and Aggression Study

– AmplitudeAmplitude First Trial Shock IntensityFirst Trial Shock Intensity Average Shock IntensityAverage Shock Intensity

Playground StudyPlayground Study– Behavioral Observation of FrequenciesBehavioral Observation of Frequencies

Group EntryGroup Entry AggressionAggression

Anger and CognitionAnger and Cognition– RT for response to different word typesRT for response to different word types

Levels of measurementLevels of measurement

Quantitative variablesQuantitative variables

– Differ in terms of amount; different values Differ in terms of amount; different values contain more or less of the variable.contain more or less of the variable.

Qualitative variablesQualitative variables

– Different values of these variables are Different values of these variables are different in quality.different in quality.

Different levels of measurement reflect Different levels of measurement reflect the degree of quantification of the the degree of quantification of the measures.measures.

NominalNominal

Differ in name (e.g.. gender, eye Differ in name (e.g.. gender, eye color).color).

Limited statistical manipulations.Limited statistical manipulations.

Mode is best summary statMode is best summary stat

Use frequencies, bar graphsUse frequencies, bar graphs

Chi-square is appropriate inferential Chi-square is appropriate inferential statstat

OrdinalOrdinal

Vary in order of quantity (e.g.. first, second, Vary in order of quantity (e.g.. first, second, and third place in a race).and third place in a race).

Non-parametric statistical analyses.Non-parametric statistical analyses. Descriptive StatisticsDescriptive Statistics::

frequency distributionfrequency distributionmean, median, modemean, median, mode

Inferential StatisticsInferential Statistics::tt test, analysis of variance (parametric) test, analysis of variance (parametric)Wilcoxin rank-sum test, Kruskal-Wallace Wilcoxin rank-sum test, Kruskal-Wallace analysis of variance (nonparametric)analysis of variance (nonparametric)

IntervalInterval

The intervals between the values of the The intervals between the values of the variables are equal (e.g.. IQ scores).variables are equal (e.g.. IQ scores).

Can use parametric statistical analyses.Can use parametric statistical analyses.– Descriptive statisticsDescriptive statistics::

frequency distributionfrequency distributionmean, median, modemean, median, mode

– Inferential StatisticsInferential Statistics::tt test testanalysis of varianceanalysis of variance

RatioRatio

– Like interval variables but with a true Like interval variables but with a true zero point (e.g.. temperature in Kelvin).zero point (e.g.. temperature in Kelvin).

– Can use the greatest variety of Can use the greatest variety of statistical analyses.statistical analyses. Descriptive statisticsDescriptive statistics::

frequency distributionfrequency distributionmean, median, modemean, median, mode

Inferential StatisticsInferential Statistics::tt test testanalysis of varianceanalysis of variance

The importance of precision in The importance of precision in measurementmeasurement

In descriptive research, precise In descriptive research, precise measurements can improve the measurements can improve the accuracy of our description of a accuracy of our description of a population.population.

When testing a research hypothesis, When testing a research hypothesis, precision increases our chances of precision increases our chances of finding a statistically significant result.finding a statistically significant result.

Measures should be as precise as Measures should be as precise as possible.possible.

Reliability of measurementReliability of measurement Reliable measures are repeatable.Reliable measures are repeatable. Test-retest reliability – Test-retest reliability – determined by determined by

correlating the scores received by a group of correlating the scores received by a group of participants who were tested at two different participants who were tested at two different times.times.

Split-half reliabilitySplit-half reliability – determined by – determined by correlating half the items on a set of correlating half the items on a set of homogeneous questions with the other half.homogeneous questions with the other half.

Inter-rater reliabilityInter-rater reliability – measures the level – measures the level of agreement between judges scoring of agreement between judges scoring behavior.behavior.

Validity of measurementValidity of measurement

Face validityFace validity

– Whether the measure seems to be a Whether the measure seems to be a reasonable measure of the variable.reasonable measure of the variable.

Construct validityConstruct validity

– Whether the measure is measuring the Whether the measure is measuring the underlying construct.underlying construct.

– Determined by how well the measure of Determined by how well the measure of a variable fits into a theory.a variable fits into a theory.

Validity of measurementValidity of measurement

Content validityContent validity– The degree that a measure assesses all The degree that a measure assesses all

the dimensions of the construct.the dimensions of the construct. Criterion and predictive validityCriterion and predictive validity

– If a measure of behavior has criterion If a measure of behavior has criterion validity then it should correlate with validity then it should correlate with another measure of the same kind of another measure of the same kind of behavior, a criterion measure.behavior, a criterion measure.

Tests, scales, and Tests, scales, and inventoriesinventories

TestTest – – refers to many procedures used to refers to many procedures used to measure a variable.measure a variable.

ScaleScale – – refers to a measure of a specific refers to a measure of a specific psychological characteristic.psychological characteristic.

InventoryInventory – – used to describe interests or used to describe interests or personality.personality.

Commercially available Commercially available tests and inventoriestests and inventories

Standardized tests of intelligenceStandardized tests of intelligence

– Stanford-Binet Intelligence Scale (SBIS)Stanford-Binet Intelligence Scale (SBIS)

– Wechsler Intelligence Scale for Children Wechsler Intelligence Scale for Children (WISC)(WISC)

– Wechsler Adult Intelligence Scale (WAIS)Wechsler Adult Intelligence Scale (WAIS)

– Woodcock-Johnson Test of Cognitive Woodcock-Johnson Test of Cognitive AbilitiesAbilities

– many moremany more

Commercially available Commercially available tests and inventoriestests and inventories

Tests of personalityTests of personality– Standardized testsStandardized tests

MMPIMMPI Millon Clinical Multiaxial Inventory (MCMI)Millon Clinical Multiaxial Inventory (MCMI) Sixteen Personality Factor Questionnaire Sixteen Personality Factor Questionnaire

(16PF)(16PF) California Psychological Inventory (CPI)California Psychological Inventory (CPI)

– Projective tests of personalityProjective tests of personality Holtzman Inkblot Technique (HIT)Holtzman Inkblot Technique (HIT) Rorschach Inkblot testRorschach Inkblot test Thematic Apperception Test (TAT)Thematic Apperception Test (TAT)

Commercially available Commercially available tests and inventoriestests and inventories

Other specialized testsOther specialized tests

– Bayley Scales of Infant Development Bayley Scales of Infant Development (BSID)(BSID)

– Yesavage Geriatric Depression Scale Yesavage Geriatric Depression Scale (GDS)(GDS)

– Young Mania Rating Scale (YMRS)Young Mania Rating Scale (YMRS)

– many moremany more