Single-subject design is best described as focusing on:

• A. An individual client's change over time
• B. Comparing group averages
• C. Analyzing population-level trends
• D. Evaluating random samples from the population

Answer: (A)

Single-subject design focuses on how one client's behavior or outcomes change over time in response to an intervention, using repeated measurements within the same individual. This approach treats the person as their own control, allowing you to observe a clear pattern of improvement, stability, or decline tied to the treatment, rather than relying on averages across many people. For example, you might track a client’s anxiety levels across baseline, during therapy, and after a treatment change to see if the intervention produces a functional change within that person. The goal is to demonstrate a relationship between the intervention and observed change within the individual. The other options describe group comparisons, population trends, or sampling methods, which are not the focus of single-subject design.