Categorical variables are variables that are not numerical. They do not derive from measurement operations (and do not have units of measurement), but from classification and comparison operations; for instance, they describe data that fits into specific categories. Categorical variables can be further grouped as nominal, dichotomous, or ordinal:
- Nominal variables are variables that have two or more categories but do not have an intrinsic order. For example, the blood group variable, limited to the ABO system, can assume the values A, B, AB, and O. If we try to sort the values that this variable can assume (for example, from smallest to largest), we immediately realize that there is no solution. These variables cannot ...
