Validation of Clinically Significant Effect Size Indices in Single-case Designs

Background: The aim of the study was to examine the validity of clinically significant effect size (CSES) indices proposed by Sanz and García-Vera (2015) for data analysis of single-case designs. The CSES indices bring together nonoverlap effect size (NES) indices with the statistical approach to clinical significance of Jacobson and Truax. Method: A total of 30 patients with posttraumatic stress disorder who had received psychological treatment were assessed using multiple measures of posttraumatic stress symptomatology. Correlational analyses were conducted to examine the association between CSES indices and three NES indices (PND, PEM, and NAP), as well as with two therapeutic success criteria at posttreatment. Results: CSES indices were found to correlate significantly with the NES indices (r = .48-1.00) and with the two posttreatment criteria (r = .37-|.62|). Conclusions: These results support the convergent and criterion validity of the CSES indices for data analysis of single-case designs.