Chapter 9 is devoted to issues of data analysis, and aims to determine if the intervention has been effective. The two main approaches to data evaluation are covered: visual analysis of graphed data and statistical techniques. The steps involved in conducting a structured visual analysis are enumerated, along with the advantages and disadvantages of the visual analysis approach. Statistical approaches are then covered, commencing with discussion of the issue of autocorrelation in SCED data. A broad range of specific statistical techniques are described, including multiple methods to calculate effects sizes, non-overlap techniques, regression-based techniques, time-series analyses, and randomisation tests. Formulae are provided where appropriate. The chapter concludes with evaluation of the intervention’s clinical significance, its social validity, and considerations regarding social impact.