Title: Interval
Course: UGQuants (SSPS) > Section: Introduction to Quantitative Analysis

Interval

With an interval level of measurement, the values of a variable not only have a logical order to them in which each value can be described as higher and/or lower than another: unlike ordinal variables, we can also say that the unit difference between any pair of adjacent values is equal. But, unlike ratio variables, we cannot say that there is a meaningful arithmetic relationship between the values. In fact in social and political research we rarely encounter variables that may be measured at an interval level but do not also meet the criteria for the ratio level of measurement. For a clear example of an interval variable that is not also a ratio variable, albeit one from beyond the social and political world, think of measuring temperature in degrees Celsius. We are able to say that the difference between 10˚C and 20˚C is the same as that between 20˚C and 30˚C, but we cannot say that 20˚C is ‘twice as warm’ as 10˚C, or that 30˚C is ‘three times as warm’ as 10˚C. It is however possible to argue that some scales used in social and political research might be (and sometimes are) interpreted as measuring at the interval but not ratio level.