Describe the fundamental flaw that prevents a pre-post design from being a true experiment. (That is, why can't these designs produce an unambiguous cause-and-effect explanation?) Explain how the series of observations before the treatment help reduce this problem

Question

What will be an ideal response?

Answer 1

The basic flaw with a pre-post design is that the observations take place over time, which means that other events that change over time have an opportunity to influence the results. For example, a typical time-series study compares observations before treatment with observations after treatment. Although the treatment may be responsible for causing a difference between the two sets of observations, it also is possible that other, time-related factors may have caused the scores to change. Thus, there are always two possible explanations for the differences that are found in a time-series study. This problem is reduced if the study uses a series of observations before the treatment is administered. If outside factors such as history or maturation are influencing the scores, the influence should be seen in the pretest series of observations. If there are no differences among the pretest observations, you can be more confident that outside factors are not affecting the data.