The results as presented do not represent a true experiment because there is no control over extraneous variables. In particular, it is possible that factors other than the treatment are responsible for the apparent change in behavior.
Variables outside the study such as the weather, changes in the student’s family situation, or changes in the student’s relationships with peers, may be responsible for causing the change in behavior. Because the study cannot measure or control all these poten- tially confounding variables, it is impossible to interpret the results as a clear, unambiguous demonstration of the treatment’s effectiveness.
To demonstrate a cause-and-effect relationship, single-subject designs must demonstrate convincingly that it is the treatment, not coincidental extraneous variables, causing the changes in behavior.