Variable

A variable is any characteristic that can differ from one observation to another — for example a person's height, a customer's city, or whether an email was opened. In a data table, each column is usually a variable and each row is one observation.

Variables are the raw vocabulary of a dataset, and the first question to ask of any new dataset is “what does each variable mean, and what could its values be?” Many analysis mistakes trace back to misunderstanding a variable — for instance treating a ZIP code as a number to be averaged when it is really a label.