Numerical (quantitative) variables have magnitude and units, with values that carry an equal weight. For example, the difference between 1 and 2 on a numeric scale must represent the same difference as between 9 and 10. There are two major scales for numerical variables:
- Discrete variables can only be specific values (typically integers). For example:
- number of siblings
- year of birth
- Continuous variables can take on any real number value. For example:
- height
- temperature
Categorical (qualitative) variables have values that describe labels or attributes. Even if the categories can be placed in a natural order, they have no magnitude or units. There are two major scales for categorical variables:
- Nominal variables have categories with no distinct or defined order. For example:
- gender
- favorite color
- nationality
- Ordinal variables have an inherent order. For example:
- Likert scales (strongly disagree, disagree, neutral, agree, strongly agree)
- t-shirt size (small, medium, large)
Note: Ordinal categorical variables are often aggregated to create scales in humanities research and can be treated as numeric if they have a sufficient amount of variation in values.