ABSTRACT
A basic tenet of behavioral science is that people differ from one another, and one goal of behavioral science is to determine the causes and effects of these differences. To study why people differ, you must fi rst be able to state the ways in which people differ (identify the important variables) and state the degree to which they differ on these variables. To study variables, you must fi rst observe them (detect their presence) and then measure them (assign numbers to them that represent the degree to which they are present). Measurement consists of the sets of procedures we use to assign numbers to (to quantify) variables.
