How do you defend an experimental study without a control group?
Nothing to defend. It is just that you have to limit the generalizability of your interpretations. What you have found in your study pretains to those two groups. The question is whether you can say something more than that. In other words, generalize your findings to people everywhere. If you do, then you will have to consider the implications of a lack of a control group. Perhaps you have some indirect way to suggest what the performance of a control group would be (other similar studies, common sense), but keep in mine it is just speculation since the control group was not exposed to the same experimental conditions. In general, control groups a very very valuable, but not always practically possible in a experimental design. Most good write ups include a self-critique of a study or more accurately, a way to design a study in the future to expand your current efforts (e.g. to include a control group).
