In an A-B-A-B single-subject design, what does the B phase represent?

• A. Post-treatment measurements.
• B. Baseline measurements.
• C. Post-treatment measurements during the B phase.
• D. Follow-up measurements.

Answer: (C)

This item is about how an A-B-A-B single-subject design uses phases to show the effect of an intervention. In this design, you establish a baseline (A), apply the treatment (B), withdraw the treatment (A), and then reintroduce the treatment (B). The B phase specifically is the period when the intervention is in place and data are collected to see whether the target behavior changes compared with baseline. It’s not a post-treatment interval; outcomes during B reflect the impact of the treatment while it is active. The subsequent A phase serves as withdrawal to test reversibility, and the final B reintroduces the treatment to confirm that the change reappears if the intervention is reapplied.