What is the defining characteristic of an interval scale of measurement?

The defining characteristic of an interval scale of measurement is that it allows for ordered ranks and equally spaced intervals. This means that not only can the values be ranked in a meaningful way from lowest to highest, but the differences between those values are also consistent and meaningful. For example, in temperature measured in Celsius, the difference between 20 degrees and 30 degrees is the same interval as that between 10 degrees and 20 degrees. This consistency allows for the application of arithmetic operations, such as addition and subtraction, but does not include a true zero point, which distinguishes it from a ratio scale.

While a true zero point is a feature of a ratio scale, options referring to mutually exclusive categories and a specific number of scores pertain to nominal and ordinal scales, respectively, and do not apply to the defining attributes of an interval scale. Thus, the characteristic of having ordered ranks with equal spacing is crucial in defining an interval scale.