Chapter 5 Measuring Variables

From Hypothesis to Design One of the first steps in designing an experiment is to operationally define the variables. One of the first steps in designing an experiment is to operationally define the variables. –IV – The causal variable  There must be at least two different levels of the independent variable. –Presence (experimental treatment) vs. absence (control condition), or can have multiple levels –The differences are in AMOUNT or TYPE –Control Variables – Those that need to be held constant across levels of the IV –DV – The effect/outcome variable

Operational Definition An explicit definition in terms that can be used to operate the research design An explicit definition in terms that can be used to operate the research design Operational definitions allow other researchers to replicate research exactly. Operational definitions allow other researchers to replicate research exactly. Operational definitions can be found by searching the literature. Operational definitions can be found by searching the literature. For a dependent variable, the operational definition is a precise description of how it is measured. For a dependent variable, the operational definition is a precise description of how it is measured.

Ways of asking questions Fixed alternative questions Fixed alternative questions –Questions where the respondent selects his or her answer from a set of specified responses. Open-ended questions Open-ended questions –Allows the respondent to provide his or her answer in his or her own words. –Often summarized with content analysis. Rating Scales Rating Scales –Fixed alternative questions where the respondent indicates magnitude on a scale.

Ways of asking questions Likert Scales Likert Scales –Statements in which the respondent is asked to indicate the degree he or she agrees or disagrees with the statement. Semantic Differential Semantic Differential –The respondent rates words on a series of bipolar scales. –Designed to measure the psychological distance between the connotative meanings of words.

Example Alcohol and Aggression Alcohol and Aggression –Social Information Processing Studies  Free Response –What do we do with the answers? –Validity  Item Rating –How does this map onto behavior?

Social desirability and response set Socially desirable responding – giving answers that respondents think are appropriate or that they think the researchers might want to hear Socially desirable responding – giving answers that respondents think are appropriate or that they think the researchers might want to hear Response set – giving only moderate answers or always agreeing or disagreeing. Response set – giving only moderate 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. –Stressing anonymity. –Including irrelevant items.

Before voting I thoroughly investigate the qualifications of all the candidates. Before voting I thoroughly investigate the qualifications of all the candidates. I never hesitate to go out of my way to help someone in trouble. I never hesitate to go out of my way to help someone in trouble. It is sometimes hard for me to go on with my work if I am not encouraged. It is sometimes hard for me to go on with my work if I 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 succeed in life. On occasion I have had doubts about my ability to 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 out in a restaurant. My table manners at home are as good as when I eat out in a restaurant. If I could get into a movie without paying and be sure I was not seen, I would probably do it. If I could get into a movie without paying and be sure I was not seen, I would probably do it. On a few occasions, I have given up doing something because I thought too little of my ability. On a few occasions, I have given up doing something because I thought too little of my ability.

Measuring observed behavior Typical ways that psychologists measure observable behavior: Typical ways that psychologists measure observable behavior: –Accuracy – responses are either right or wrong. –Frequency – how often a behavior occurs in a specified period of time. –Latency – speed of onset. –Duration – how long the behavior lasts. –Amplitude – size of response. –Choice selection – frequency of choice between alternatives.

Example Alcohol and Aggression Study Alcohol and Aggression Study –Amplitude  First Trial Shock Intensity  Average Shock Intensity Playground Study Playground Study –Behavioral Observation of Frequencies  Group Entry  Aggression Anger and Cognition Anger and Cognition –RT for response to different word types

Levels of measurement Quantitative variables Quantitative variables –Differ in terms of amount; different values contain more or less of the variable. Qualitative variables Qualitative variables –Different values of these variables are different in quality. Different levels of measurement reflect the degree of quantification of the measures. Different levels of measurement reflect the degree of quantification of the measures.

Nominal Differ in name (e.g.. gender, eye color). Differ in name (e.g.. gender, eye color). Limited statistical manipulations. Limited statistical manipulations. Mode is best summary stat Mode is best summary stat Use frequencies, bar graphs Use frequencies, bar graphs Chi-square is appropriate inferential stat Chi-square is appropriate inferential stat

Ordinal Vary in order of quantity (e.g.. first, second, and third place in a race). Vary in order of quantity (e.g.. first, second, and third place in a race). Non-parametric statistical analyses. Non-parametric statistical analyses. Descriptive Statistics: frequency distribution mean, median, mode Descriptive Statistics: frequency distribution mean, median, mode Inferential Statistics: t test, analysis of variance (parametric) Wilcoxin rank-sum test, Kruskal-Wallace analysis of variance (nonparametric) Inferential Statistics: t test, analysis of variance (parametric) Wilcoxin rank-sum test, Kruskal-Wallace analysis of variance (nonparametric)

Interval The intervals between the values of the variables are equal (e.g.. IQ scores). The intervals between the values of the variables are equal (e.g.. IQ scores). Can use parametric statistical analyses. Can use parametric statistical analyses. –Descriptive statistics: frequency distribution mean, median, mode –Inferential Statistics: t test analysis of variance

Ratio –Like interval variables but with a true zero point (e.g.. temperature in Kelvin). –Can use the greatest variety of statistical analyses.  Descriptive statistics: frequency distribution mean, median, mode  Inferential Statistics: t test analysis of variance

The importance of precision in measurement In descriptive research, precise measurements can improve the accuracy of our description of a population. In descriptive research, precise measurements can improve the accuracy of our description of a population. When testing a research hypothesis, precision increases our chances of finding a statistically significant result. When testing a research hypothesis, precision increases our chances of finding a statistically significant result. Measures should be as precise as possible. Measures should be as precise as possible.

Reliability of measurement Reliable measures are repeatable. Reliable measures are repeatable. Test-retest reliability – determined by correlating the scores received by a group of participants who were tested at two different times. Test-retest reliability – determined by correlating the scores received by a group of participants who were tested at two different times. Split-half reliability – determined by correlating half the items on a set of homogeneous questions with the other half. Split-half reliability – determined by correlating half the items on a set of homogeneous questions with the other half. Inter-rater reliability – measures the level of agreement between judges scoring behavior. Inter-rater reliability – measures the level of agreement between judges scoring behavior.

Validity of measurement Face validity Face validity –Whether the measure seems to be a reasonable measure of the variable. Construct validity Construct validity –Whether the measure is measuring the underlying construct. –Determined by how well the measure of a variable fits into a theory.

Validity of measurement Content validity Content validity –The degree that a measure assesses all the dimensions of the construct. Criterion and predictive validity Criterion and predictive validity –If a measure of behavior has criterion validity then it should correlate with another measure of the same kind of behavior, a criterion measure.

Tests, scales, and inventories Test – refers to many procedures used to measure a variable. Test – refers to many procedures used to measure a variable. Scale – refers to a measure of a specific psychological characteristic. Scale – refers to a measure of a specific psychological characteristic. Inventory – used to describe interests or personality. Inventory – used to describe interests or personality.

Commercially available tests and inventories Standardized tests of intelligence Standardized tests of intelligence –Stanford-Binet Intelligence Scale (SBIS) –Wechsler Intelligence Scale for Children (WISC) –Wechsler Adult Intelligence Scale (WAIS) –Woodcock-Johnson Test of Cognitive Abilities –many more

Commercially available tests and inventories Tests of personality Tests of personality –Standardized tests  MMPI  Millon Clinical Multiaxial Inventory (MCMI)  Sixteen Personality Factor Questionnaire (16PF)  California Psychological Inventory (CPI) –Projective tests of personality  Holtzman Inkblot Technique (HIT)  Rorschach Inkblot test  Thematic Apperception Test (TAT)

Commercially available tests and inventories Other specialized tests Other specialized tests –Bayley Scales of Infant Development (BSID) –Yesavage Geriatric Depression Scale (GDS) –Young Mania Rating Scale (YMRS) –many more