What is the primary aim of Single Subject Designs?

• A. To examine causal effects in large populations
• B. To determine whether an intervention has the intended impact on an individual or a small group
• C. To compare outcomes across randomized groups
• D. To measure the prevalence of a trait in a population

Answer: (B)

Single Subject Designs aim to show that a specific intervention produces the intended change in a target behavior for one person (or a very small group) by tracking that behavior repeatedly over time across different phases. The strength lies in demonstrating a functional relation within the individual: when the intervention is applied, the behavior changes in a consistent, predictable way, and when it is removed or altered, the behavior tends to revert or shift accordingly. This approach emphasizes causal inference at the individual level and is ideal for determining whether an intervention works for a particular person, guiding personalized treatment. It differs from studies that look at effects across large populations, compare randomized groups, or measure how common a trait is in a population.