What is the major problem with the nonequivalent control group design?
The correct answer and explanation is:
The major problem with the nonequivalent control group design is the lack of random assignment to the treatment and control groups. In this design, participants are not randomly assigned to the groups, which makes it more difficult to ensure that the groups are comparable at the outset of the study. Without random assignment, there is a higher risk that the groups may differ in ways other than the treatment, such as in pre-existing characteristics or other variables that could influence the outcome.
Because of this, any differences observed between the groups after the intervention could be due to these pre-existing differences, rather than the treatment itself. This makes it harder to establish a clear cause-and-effect relationship. The potential for selection bias is significant because the groups might already differ in important ways before the treatment begins, leading to inaccurate conclusions about the treatment’s effectiveness.
For example, in an education study, if students who are more motivated are assigned to the treatment group while less motivated students are placed in the control group, the observed improvement in the treatment group may be due to their higher motivation levels rather than the specific intervention being tested.
To mitigate this issue, researchers might use statistical controls or matching techniques, where participants in the control group are matched with participants in the treatment group based on key characteristics. However, this still doesn’t completely eliminate the possibility of bias, and results from a nonequivalent control group design are generally considered less reliable than those from a randomized controlled trial (RCT). The lack of random assignment is the primary limitation of this design, making it difficult to draw definitive conclusions about causal relationships.