Which research design is most informative for determining whether an intervention caused observed change in a single participant?

• A. Randomized controlled trial
• B. Cross-over design
• C. ABAB or ABA design
• D. Case-control study

Answer: (C)

This item is about proving that an intervention actually caused a change in one person’s behavior. ABAB or ABA designs are best for this because they manipulate the conditions and track the same individual across multiple phases. Start with a baseline to establish the behavior’s level before any intervention. Then apply the intervention and observe what changes occur. After a withdrawal phase, remove the intervention to see if the behavior returns toward baseline. In ABAB, you reintroduce the intervention to see if the change reappears. This back-and-forth, with repeated measurements in the same person, provides a clear link between the intervention and the observed change, strengthening the case that the intervention caused the effect rather than other factors like maturation, history, or outside events.

Other designs don’t establish causal control as clearly for a single participant. Randomized controlled trials involve groups and randomization, making it difficult to attribute changes to the intervention for one person alone. A cross-over design compares two treatments within the same individual but can suffer from carryover effects and doesn’t always include deliberate withdrawal to demonstrate a functional relation. Case-control studies are observational and retrospective, not suited for showing causality within a single subject.