What is the primary feature of a reversal design (ABAB design)?

The primary feature of a reversal design, often referred to as an ABAB design, is the systematic application and withdrawal of treatment phases. This design typically consists of alternating between a baseline phase (A) and a treatment phase (B). By reintroducing and withdrawing the treatment, the therapist can observe the impact of the intervention on the subject's behavior more clearly. This method allows for strong causal inferences, illustrating whether changes in behavior correspond to the introduction or removal of the treatment.

This approach is particularly useful in evaluating the effectiveness of interventions, as it provides clear evidence for the relationship between the treatment and behavioral changes over time. The alternating phases enhance the reliability of the results, and the repeated measures can confirm whether the observed effects are consistent or temporary.

The other options do not capture this fundamental aspect of a reversal design. Assignment to multiple treatment groups, simultaneous analysis of behaviors, or focusing on a singular treatment phase diverges from the essential characteristic of rhythmically alternating treatment and control conditions that define the ABAB design.