Sampling

A population is the whole set of items that are of interest.

A census observes or measures every member of a population.

A sample is a selection of observations or measurements taken from a subset of the population, used to find out information about the population.

A sampling unit is an individual member of a population.

A sampling frame is a numbered list of sampling units of a population.

Variables

Quantitative variables or data are numerical in nature, such as height or weight.

Qualitative variables or data are non-numerical in nature, such as colours of cars.

A continuous variable can take any value in a given range, such as height or weight.

A discrete or discontinuous variable can only take specific values in a given range, such as rolling numbers on a dice.