In which design does behavior first get observed without treatment before any interventions are introduced?

The correct answer is the reversal design, which is used in experimental research to observe the effects of an intervention on a specific behavior. In this design, behavior is first assessed during a baseline phase, where no treatment or intervention is applied. This initial observation allows for a clear understanding of the behavior prior to any influence from the therapy or intervention being studied.

Once baseline data is collected, the intervention is introduced, and the behavior is observed again. This allows for comparisons between the baseline (no treatment) and the intervention phases. This approach not only establishes a clear measure of the behavior without treatment but also provides evidence for the effectiveness of the intervention by observing changes in behavior in response to it.

The other design options focus on different aspects of observation or experimental manipulation. For instance, in experimental design variations, treatments are typically assigned to groups but may not specifically highlight the initial baseline observation without treatment. Case study design is more qualitative and focuses on an in-depth exploration of a single subject or situation, often without systematic manipulation or observation of behavior without treatment. Repeated measures design involves taking measurements at multiple points, but it does not specifically highlight the observation of behavior before any treatments are introduced. Thus, the reversal design is the most appropriate for this specific scenario.