Categories with different names, ex. gender, religious affiliation. Qualitative not quantitative differences between categories (no information on order of magnitude of categories) Categories ranked by size or magnitude, ex. Know order/rank of objects, but no information about size of intervals between ranks. Ordered categories with intervals of equal size. No rational (or absolute) zero point, ex. Ordered categories with intervals of equal size and absolute zero point, ex. I y age y gender y occupation y anxiety level y y y number of children r y height y weight y hair colour level of education can be r or o. Observe two variables for each individual to determine whether there is a relationship between them (i. e. , whether the variables change together). Comparing two (or more) groups of scores to find differences between the groups. One variable defines the group, the other variable is measured to create scores for the group.