The impact of baseline trend control on visual analysis of single-case data

The impact of baseline trend control on visual analyses of AB intervention graphs was examined with simulated data at various values of baseline trend, autocorrelation, and effect size. Participants included 202 undergraduate students with minimal training in visual analysis and 10 graduate students and faculty with more training and experience in visual analysis. In general, results were similar across both groups of participants. Without statistical adjustments to correct for baseline trend, Type I errors greatly increased as baseline trend increased. With corrections for baseline trend, fewer Type I errors were made. As trend increased, participants made fewer Type II errors on the unadjusted graphs as compared to the graphs with baseline trend control. The greater Type II error rate on adjusted graphs could be an artifact of study design (i.e., participants did not know if baseline trend control had been applied), and the impact of MASAJ on Type II errors needs to be explored in detail prior to more widespread use of the method. Implications for future use of baseline trend control techniques by educational professionals are discussed.