Measurement of Variables

1. Measurement of Variables • What are the Four Types of Psychological Measures? • What are the Four Measurement Scales? • What are Discrete and Continuous Variables?

2. Types of Measures • Self-Report • Tests • Behavioral Measures • Physical Measures

3. Measurement Scales • The measurement scale tells you what assumptions you can make about a score. • Many statistics require a certain measurement scale. • The measurement scale is a property of the data, not a decision made by the researcher.

4. Nominal Scale • Numbers classify into groups. • Math, other than counting, is not meaningful. • EXAMPLES: • gender • hair color

5. Ordinal Scale • Numbers are rank orders. • Most mathematical operations are not meaningful. • EXAMPLES: • order of finish in a race • class rank

6. Interval Scale • Numbers represent amounts, with equal intervals between numbers. • Math, other than ratio comparisons, is meaningful. • EXAMPLES: • score on intelligence test • temperature in Celsius

7. Ratio Scale • Numbers represent amounts, with equal intervals and an absolute zero • absolute zero: zero represents complete absence • Math, including ratios, is meaningful. • EXAMPLES: • number of seconds to finish • temperature in Kelvin

8. Why You Can’t do Ratios on an Interval Scale

9. The Same Temperatures on Another Interval Scale

10. The Same Temperatures with Absolute Zero Shown

11. The Same Temperatures on a Ratio Scale (Rankine = F + 459.6)

12. The Same Temperatures on a Ratio Scale (Kelvin = C + 273.15)

13. Discrete vs. ContinuousVariables • discrete: separate, whole number values • EXAMPLE: number of pets • continuous: continuum including fractional values • EXAMPLE: height

14. Real Limits • A score on a continuous variable is really an interval. • The real limits are half a unit down and half a unit up from the measured score. • measured score = 65 inches • real limits: 64.5-65.5 inches