Which study design is most limited due to the absence of a control group?

• A. Cross-Sectional Survey
• B. Randomized Controlled Trial
• C. Case-Control Study
• D. Single-Group Pretest-Posttest Design

Answer: (D)

The main issue here is the need for a control group to determine whether observed changes are actually due to the intervention or to other factors. In a single-group pretest-posttest design, you measure an outcome before and after the intervention in the same group, but there is no separate comparison group. Without that comparison, any observed change could be caused by maturation, history, regression to the mean, or placebo effects, not necessarily the intervention itself. This makes it difficult to draw causal conclusions. Other designs include built-in comparisons: cross-sectional surveys provide a single snapshot and can’t establish that the exposure occurred before the outcome; randomized controlled trials include a control group and randomization, strengthening causal inference; case-control studies compare people with and without the outcome, effectively using a control group for comparison. The lack of a control group is what limits the single-group pretest-posttest design the most.