Which study design looks backward in time to determine outcomes?

The correct answer is the case control study because this study design specifically looks backward in time to identify and compare individuals with a particular outcome (often referred to as cases) to those without that outcome (the controls). Researchers investigate past exposures or risk factors to determine if they are associated with the outcome of interest.

In contrast, a randomized clinical trial involves assigning participants to groups to test interventions prospectively, which means it looks forward from the point of intervention to assess outcomes. A cohort study also follows individuals over time, starting with an exposed group and a non-exposed group, to observe outcomes. This study design is longitudinal and examines events as they unfold from a defined starting point going forward. A cross-sectional study, on the other hand, captures data at a single point in time, evaluating both exposure and outcome simultaneously without regard to the timing of events.

Thus, among all the options, the case control study is distinct in its retrospective approach, making it the appropriate choice for this question.