Defining and Measuring Variables

1. Defining and Measuring Variables Chapter 4 George S. Robinson, Jr., Ph.D. Department of Psychology North Carolina A&T State University

2. Constructs • Construct • a hypotheticalattribute or mechanism that helps explain of predict behavior in a theory • external stimulus factors --> Construct --> behavior • examples • intelligence • love • patriotism

3. Operational Definition • Operational definition • a procedure for measuring and defining a construct • examples • The Effects of Food Deprivation on Maze Learning in Rats • The Relationship Between War and Patriotism • Investigating Part-time Work in College Students on Classroom Sleeping

4. Validity • Validity • the degree to which the measurement process measures the variable it claims to measure • examples • IQ • Job Satisfaction • Mechanical Ability

5. Types of Validity • Face validity • when a measure superficially appears to measure what it claims to measure • Concurrent validity • when scores obtained from a new measure, are directly related to scores from a more established measure of the same variable

6. Types of Validity - cont. • Predictive validity • when scores from a measure accurately predict behavior according to a theory • Construct validity • when scores from a measure are directly related to the variable itself • Convergent validity • is demonstrated by a strong relationship between the scores obtained from two different methods of measuring the same construct • Divergent validity • is demonstrated by using two different methods to measure two different constructs.

7. Reliability • Reliability • the stability or consistency of the measurement • Examples • IQ • Job Satisfaction • Mechanical Ability • measure score = true score + error • observer error - the person making the measurement can create error • environmental changes - changes in the environment can create error • participant changes - changes in the participant can create error

8. Types of Reliability • Test-retest reliability (successive measurements) • same measurement at two different times • Inter-rater reliability (simultaneous measurements) • two or more observers who simultaneously record measurements • Split-half reliability (internal consistency) • split a set of items in half, and compute a score for each half

9. Scales of Measurement • Nominal scale • qualitative difference in the measured variable • example: gender, classification, major • Ordinal scale • ranked categories • example: top ten songs • Interval scale • organized sequentially and all categories are the same size, equal intervals • example: temperature, seconds, weight • Ratio scale • equal ordered categories with a true zero point • example: heart rate, blood pressure, brainwaves

10. Modalities of Measurement • Self-Report Measures • the participants describe or report • types of questions • open-ended questions • restricted questions • rating scale questions • Likert-type scale • 1 - strongly disagree, 2 - disagree, 3 - undecided, 4 - agree, 5 - strongly agree • anchors - verbal labels (e.g., strongly agree) • response set - tendency to answer all questions the same • semantic differential - rate how well the adjective describes you

11. Modalities of Measurement - cont. • Physiological measures • behavioral measures • frequency method • duration method • interval method • time sampling • event sampling • individual sampling • content analysis • archival research

12. Other Aspects of Measurement • Multiple measures • use two or more procedures to measure the same variable • sensitivity and range effects • ceiling effect - cluster of scores at the high end of the measurement scale • floor effect - cluster of scores at the low end of the scale • Participant reactivity and experimental bias • demand characteristics • reactivity • single-blind • double-blind