Interval Scale
aka "Equal Interval Scale"


Numbers are assigned to events to describe how different two events are.

At this level we have

Some Examples

Meaningful Operations

Equality (nonequality) operation: See Nominal Scale.

Greater (Lesser) operation: See Ordinal Scale

Addition (Subtraction) operations

Because we have a unit of measure, we can determine which differences are larger and which differences in events are smaller.

We can also talk about ratios of differences. The difference in temperature from 40° to 50° is twice the difference in temperature from 60° to 65°.

Measure of Central Tendency

Mode: See Nominal Scale

Median: See Ordinal Scale

Mean: The mean is the number that "balances" the total distances of scores less than the mean with the total distances of scores greater than the mean.

The mean is the number that makes the total of the positive deviations the same as the total for the negtive deviations

Score Mean Deviation
5
- 11
- 6
5
-11
- 6
10
- 11
- 1
15
- 11
4
20
- 11
9
The negative deviations total the same as the positive deviations and thus balance out (+13 and -13).
To do the balancing, you have to know how far the scores are from the mean. You can't do that unless you have a unit of measure so you can count the number of units of measure the two events are.

Is Intelligence measured at the interval level?


© 2002 by BurrtonWoodruff. All rights reserved. Modified Thursday, June 6, 2002