Trend line influence on visual analysis of single-subject data in rehabilitation research

Single-subject design and n of 1 randomized clinical trials are being advocated as methods of conducting clinical research in rehabilitation environments. The traditional procedure for interpreting data from such designs is visual analysis. This study examined the effect of including trend lines on the visual judgements made from single-subject data. Twenty-four hypothetical single-subject A-B designs were presented to 20 rehabilitation therapists for visual interpretation. The graphs represented traditional single-subject designs, including a baseline and treatment phase. Trend lines were computed and included in both phases of the design as an adjunct to visual analysis. The interrater reliability of the visual judgements was calculated using the intraclass correlation coefficient and ranged from 0.54 to 0.90. The results suggest that adding trend lines to graphed data presented in single-subject designs can improve the consistency of visual judgements. Implications for using adjuncts to graphing data points in single-subject rehabilitation research are discussed.