Reliability, convergent and structural validity and cut-off score of the Severity of Dependence Scale for recreational ketamine users

Abstract Background and aims There is a lack of instruments for measuring ketamine substance use disorders. The aims were (i) to estimate the reliability and provide evidence of validity of the Severity of Dependence Scale (SDS) in a sample of recreational users, and (ii) propose a cut-off point to determine the presence of dependence. Methods We conducted a web-based cross-sectional survey with recreational users who accessed webs related to recreational drug use and harm reduction. 264 recreational ketamine users who had taken it in the past month participated in the study. The Spanish version of the SDS was used. Information on ketamine use-related problems and ketamine use patterns was also collected. Results The reliability estimation calculated by the Cronbach’s alpha coefficient was 0.776. SDS showed evidence of convergent validity based on relationships with other variables. Two comparisons were made in this study to analyze the Receiver Operating Characteristic Curve. For frequency of use in the last month the area under curve (AUC) was 0.835 (CI = 0.775-0.895) with optimal discrimination at an SDS score of 3. For having been in treatment for decreasing or quitting ketamine use the AUC was 0.902 (CI = 0.840-0.963) and the cut-off point was 4. Confirmatory factor analysis showed a one-dimensional structure when Items 3 and 4 were correlated. Conclusions This study has provided evidence of reliability and validity of the ketamine version of the SDS for recreational users. Considering that ketamine use is linked to young people and its strong potential for causing serious impairment, a cut-off of 3 is proposed as indicative of dependence.