Single-case analysis (A-B design)

One person (or a few) is measured repeatedly over a longer time, first without intervention (phase A, baseline), then with intervention (phase B). Group tests do not fit because the measurements follow each other and are related. Instead the phases are compared: mean and median per phase, NAP, Tau-U, baseline-corrected Tau and PND. The time-series chart shows the measurements in order, with a vertical line at the change of phase. With several people there is one chart per person (multiple baseline) and a mean across the cases.

Example: A child with special educational needs reads on average 52 words per minute during a 5-week baseline and 73 during a 15-week intervention phase.

Caution: An A-B design alone does not show a cause: maturation, chance or other events may be behind it. Replications (A-B-A-B, several people with staggered starts) are more reliable. At least 3 data points per phase, preferably 5 (What Works Clearinghouse).