When we talk about levels of measurement, we are talking about how we measure a variable. There are two broad types of variables that can be further broken into the 4 main levels of measurement:
- Categorical (qualitative) – variables where data are grouped into categories
- Nominal - levels of the variable are identifiers only. There is no inherent order to the categories.
- Examples: breed of dog, name of university, favorite food
- Ordinal - levels of the variable belong in a specific order
- Examples: grade in school, position in race, rating scales
- Continuous (quantitative) – variables where data fall along a spectrum with standard intervals
- Interval - values on the scale fall at set distances, but the scale does not have a true 0 point
- Examples: composite scores, temperature
- Ratio - values on the scale fall at set distances and there is a true 0 point
- Examples: height, weight, speed, time
Note: SPSS lumps both interval and ratio into a single classification: "Scale"
The graphic below should help you visualize the four different levels of measurement. See the definitions and examples below for each.
