Optimal scaling of the CAST and of SDS Scale in a national sample of adolescents

Abstract

PurposePsychometric and screening properties of the Cannabis Abuse Screening Test (CAST) and of the Severity Dependence Scale (SDS) were investigated using DSM-IV diagnoses of cannabis dependence (CD) as external criteria. Performance of the SDS and of the CAST were compared. MethodsCross-sectional European School Survey Project on Alcohol and Other Drugs (ESPAD) was carried out in Italy in 2009. The sample consisted of 5787 Italian adolescents aged 15–19 who reported cannabis last year use. Uni-dimensionality, internal reliability, external validity, and optimal scaling of the 6 items for CAST and 5 items for SDS were performed. The Munich Composite International Diagnostic Interview (M-CIDI) was used as a gold standard for DSM-IV diagnoses, and all outputs were assessed by 10-fold cross validation procedure. ResultsBoth scales were uni-dimensional and Cronbach's α was 0.74 for SDS and 0.78 for CAST. High and comparable area under curve (AUC) values indicate a good ability of both scales to discriminate between individuals with and without dependence diagnosis. Based on balanced sensitivity and specificity, the optimal cut-off scores for problematic use disorders were 7 for CAST MCA and 4 for SDS MCA. Both CAST and SDS overestimated CD prevalence. ConclusionsThe CAST and SDS are equally useful for screening for problematic cannabis use disorders. Both clinical and research applications of the scales are possible.