We have noticed that some texts include as a quasi-experimental design the one-group pretest-posttest comparison where the researcher measures some aspect of behavior of a single group of participants once before and once after treatment

We have noticed that some texts include as a quasi-experimental design the one-group pretest-posttest comparison where the researcher measures some aspect of behavior of a single group of participants once before and once after treatment. Such an approach has a serious flaw because there is no control group, and so we cannot determine if any changes in behavior after treatment are related to the treatment. Perhaps the change might have occurred without treatment. We have no way to assess this possibility. As such, we do not consider this to be a research approach of value.