This document defines and compares four scales of measurement: nominal, ordinal, interval, and ratio. Nominal and ordinal scales are qualitative and classify variables into categories without numeric values. Interval and ratio scales are quantitative and assign numerical values, with ratio scales having a true zero point allowing ratio comparisons. Examples are provided to illustrate the characteristics and appropriate uses of each scale.

1. Scales of Measurement
Refers to the type of scale on which the DV is
measured
Certain statistics can be calculated on some
scales, but not others
Four scales
Nominal
Ordinal
Interval
Ratio
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2. Scales of Measurement
Nominal Qualitative measures – classify into
Ordinal nonnumeric categories
Interval Quantitative measures – measurement is
Ratio numerical
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3. Nominal Scale
Assign responses to different categories
No numerical difference between categories
Examples
Gender
Marital status
State of residence
College major
SSN
Zip code
Student ID
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4. Ordinal Scale
Set of categories that are ordered from least to most
Don’t know numerical distance from each category to
the next
Examples
Miss America results –
first place, runner-up, second, third
Military rank
Letter grade in class
Degrees held
Medical condition (satisfactory, serious, guarded,
critical)
Rank order of your preference from 1 to 4 of Ruffles,
Doritos, Cheetos, Fritos
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5. Interval Scale
Scale with values, and there is the same
numerical distance between each value
This scale has an arbitrary zero point (no true
meaningful zero point)
Examples
How appealing is this cereal box to children?
Not at all very
-3 -2 -1 0 1 2 3
Current temperature
Many behavioral science questionnaires
IQ
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6. Ratio Scale
Scale with scores where there is the same
numerical distance between each score
The scale has a true, meaningful zero point that
anchors the scale
Only scale that allows you to make ratio
comparisons, such as “Maribel’s income is 35%
more than Susan’s”
Examples
Weight of a package of candy
Number of times you return to a restaurant after visiting it
the first time
Amount of money in your checking account
Number of questions correct on a quiz
Distance from San Antonio to Laredo
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