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 Cant 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