And what about when two variables are correlated? What does that really mean? To make this simple, let’s start with the simplest kind of variable, a binary variable with only two possible values. Oftentimes a binary variable is the answer to a yes-or-no question: “Are you married?” “Do you smoke?” “Are you now, or have you ever been, a member of the Communist Party?” When you’re comparing two binary variables, correlation takes on a particularly simple form.
