Empirical investigation of visual-inspection versus trend-line analysis of single-subject data

We examined the inferential decisions made using either visual analysis alone or in combination with a trend line to evaluate data from single-subject research designs. Thirty-nine subjects were randomly assigned to either a Visual Group (n = 20) that used a visual-inspection approach to analyzing graphed data or a Quantitative Group (n = 19) that used a trend-line approach. After instruction in interpretation, we asked the subjects to analyze graphs containing data from five hypothetical AB single-subject designs. Results revealed a statistically significant difference in the decision made between the two groups for four of the five graphs. The group using the trend line to analyze graphed data exhibited more confidence in the decisions they made and also demonstrated greater within-group consistency as compared with the group using visual inspection. The implications of various methods of data analysis in establishing the scientific legitimacy of single-subject research methods are discussed, and the argument is made that quantitative procedures can assist in the analysis and interpretation of single-subject data.