Most evaluation is done on one program at a time.
Study is done to determine whether the participants are better off after the program than they were before it. If control groups are used, the evaluation will determine whether results are real or extraneous. Even within a single program, it is possible to do a comparison study. For example, many programs continue through a series of smaller projects and these smaller units can be evaluated with respect to differing levels of success or goal attainment. Even when the projects have the same goals and ways of delivering a program, important information can be uncovered.