Visual Analysis of Single-Case Data

Visual analysis is the primary method for judging whether an intervention produced an effect in single-case and single-system designs: the data are plotted as a time series across baseline and intervention phases and read systematically for changes in level, trend, variability, immediacy of effect, overlap between phases, and consistency across similar phases. Rooted in applied behavior analysis and codified by the What Works Clearinghouse single-case standards, it treats the graph itself as the evidence and reserves the label 'effect' for changes that are clear, replicated within the design, and unlikely to reflect ordinary fluctuation.