A variable is the building block of psychological research. It is the fundamental unit of a study. Any trait or behavior that we wish to study is translated into a variable so that we can measure it with numbers. We use the term variable because we are studying traits that vary across individuals or across time. If we want to study the relationship between red hair and school achievement, we must first operationalize our traits of interest, that is turn them into variables. We will code hair color as 1 = red hair, 0 = not red hair. We will operationalize school achievement by using grades, translating A through F into a 13-point scale, (A = 13, A = 12, A-= 11, B = 10, etc.). Having translated our traits of interest into numerical variables, we can now use mathematics to calculate the relationships between the variables. This, in effect, is the nuts and bolts of psychological science.