An interval scale of measurement consists of an ordered set of categories (as with the ordinal scale). Also, the interval scale specifies that all the intervals are the same size. That is, the spaces between points along the scale are always the same size. Take distance measured in inches for example. The distance between the 2-inch mark and the 3-inch mark on a yardstick is the exact same as the distance between the 35-inch mark and the 36-inch mark. An inch is always an inch, no matter where we find it on the scale.
The Interval Scale both orders and measures data, but does not have an absolute zero.
It is important to note that the line between the ordinal scale and the interval scale can become fuzzy when dealing with Likert Scales. For example, mean scores are often reported about levels of agreement with statements on a scale of 1 to 5.
Last Modified: 06/29/2018