ABA Reversal Method

The ABA reversal method is a single-subject experimental design in which one participant is observed across three phases: a baseline (A), an intervention (B), and a return to baseline (A). By comparing performance across the A-B-A sequence, the design isolates the effect of the intervention on that participant. Variants include ABAB and multiple-baseline designs. The approach is widely used in accessibility and assistive-technology research because rigorous evaluation of a new tool is often required with very small numbers of participants — sometimes just one — particularly when the target population is narrow (for example, users with a specific rare disability). Results are usually analysed with visual inspection of time-series data and non-parametric randomization tests.