A researcher would like to use a factorial study to compare two programs designed to help people stop smoking. The smoking behavior of each participant will be measured at the beginning of the program, at the end of the program, and again four months after the program has ended. Thus, the two treatment programs make up one factor, the three measurement times make up the second factor. For this study, which factor(s) should be between-subjects and which should be within-subjects? Explain your answer.