©1998 Brooks/Cole Publishing/ITP
There are several variables in this example. The experimental unit on which the variables are measured is a particular undergraduate student on the campus. Five variables are measured for each student: grade point average (GPA), gender, year in college, major, and current number of units enrolled. Each of these characteristics varies from student to student. If we consider the GPAs of all students at this university to be the population of interest, the five GPAs represent a sample from this population. If the GPA of each undergraduate student at the university had been measured, we would have generated the entire population of measurements for this variable.
The second variable measured on the students is gender, which can fall into one of two categories—male and female. It is not a numerically valued variable and hence is somewhat different from GPA. The population, if it could be enumerated, would consist of a set of Ms and Fs, one for each student at the university.