This document discusses the four scales of measurement used in psychological research: nominal, ordinal, interval, and ratio. Nominal scale involves mutually exclusive categories like gender. Ordinal scale involves discrete categories that can be rank ordered. Interval scale involves numerical data without a meaningful zero point, like IQ scores. Ratio scale involves numerical data with a meaningful zero point, like height. The type of scale used to measure data determines which statistical techniques can be applied in analysis.

1. Dr. Kogan, Fall 2007
Scales of Measurement
No—Oil—In—Rivers

2. Different Types of Data
 When behavior is measured in a study,
“data” or information are created.
 The measurements made in
psychological research belong to one of
four subtypes, or “scales”.
 Thus, there are also four types of data
or variables…

3. Scales of Measurement
Type of Scale
or data
Key Features Examples
Nominal Mutually exclusive
categories.
“categorical data”
Gender
Ethnicity
Yes/no Responses
Ordinal Discrete categories
that can be rank
ordered, to show more
or less of something.
Educational Level
Class Rank
Socioeconomic Status
Interval Numerical data but
without a meaningful
zero point.
Fahrenheit Scale
IQ Scores
Personality Test Scores
Ratio Numerical data plus a
meaningful zero point.
Height, Reaction Time,
# of times a behavior
occurs

4. Measuring Students’ Studying
Type of Scale Question & Method of
Measurement
Examples
Nominal
Do Students Study?
Responses fall into
“yes” or “no” categories.
Carl – yes Jeff - yes
Maria – yes Rosa - no
Neil – yes Jenna - no
Ordinal
Who studies more?
Students are rank
ordered on studying.
Carl studies more than
Maria, who studies more
than Neil, who studies
more than Jeff, etc.

5. Measuring Students’ Studying (2)
Type of Scale Question & Method of
Measurement
Examples
Interval
Who studies more?
Studying is rated on a
5-point scale.
(a Likert Scale)
Carl – 5 (Always)
Maria - 4 (Usually)
Neil – 3 (Often)
Jeff – 2 (Sometimes)
Rosa – 1 (Never)
Jenna – 1 (Never)
Ratio
Who studies more?
Measure the amount of
time spent studying.
Carl – 6 hours/day
Maria – 5 hours/day
Neil – 2 hours/day
Jeff – 1 hour/day
Rosa – 0 hours/day
Jenna – 0 hours/day

6. Why is all this important?
 The level of measurement of the data will
determine which statistical techniques will be
used in a study.
 Example: To summarize the nominal data in
the Simon & Levin study of change blindness,
a 2X2 Contingency Table is needed. You can’t
use an “average” response because the data
were categorical, not numerical.