Single-subject designs

Here's a design where one client is their own control group. Single-subject (single-case) designs let a counselor rigorously test whether this intervention works for this client — which is why they're a favorite in applied behavioral and clinical settings.

Instead of comparing a treatment group to a control group, single-subject designs compare a person to themselves over time, measuring the target behavior repeatedly across phases. The foundation is the baseline — the A phase — where you measure the behavior before any intervention, until it's stable and predictable. Baseline is the standard of comparison: without it, you can't tell whether the treatment changed anything.

Add the intervention and you get the B phase. The simplest version, an AB design, shows change but is weak — something else in the client's life might have caused the shift. So you strengthen it by withdrawing the treatment and watching what happens. That's the ABAB (reversal/withdrawal) design: A baseline, B treatment, A withdraw treatment (return to baseline), B reintroduce treatment.

The logic is elegant: if the behavior improves during each B and worsens/reverts when you withdraw in the second A, the repeated pattern makes it very unlikely that coincidence or an outside event caused it — the intervention is doing the work. This is how a single case demonstrates experimental control and a functional relationship between intervention and behavior.

Clinical utility is the selling point: you get individualized, real-time data on whether a treatment is helping a specific client, and can adjust immediately — perfect for behavior-analytic and school/clinical practice. One caution: ABAB is ethically/practically inappropriate when withdrawing treatment would be harmful (e.g., self-injury) or when a behavior, once learned, can't reverse — in those cases counselors use non-reversal alternatives such as multiple-baseline designs.

Clinical Pearl: ABAB = baseline, treatment, withdraw, reinstate. The client is their own control, and the give-take-give-back pattern is what proves the intervention (not chance) caused the change — but never withdraw a treatment when doing so would endanger the client.