1. Classification of Variables
Discrete Numerical Variable
A variable that produces a response that comes from a counting process.

2. Classification of Variables
Continuous Numerical Variable
A variable that produces a response that is the outcome of a measurement process.

3. Classification of Variables
Categorical Variables
Variables that produce responses that belong to groups (sometimes called “classes”) or categories.

4. Measurement Levels
Nominal and Ordinal Levels of Measurement refer to data obtained from categorical questions.
A nominal scale indicates assignments to groups or classes.
Ordinal data indicate rank ordering of items.