Reliability and validity of the Severity of Dependence Scale for detecting cannabis dependence in frequent cannabis users

The Severity of Dependence Scale (SDS) measures with five items the degree of psychological dependence on several illicit drugs, including cannabis. Its psychometric properties have not yet been examined in young adult frequent cannabis users, an eminently high-risk group for cannabis dependence. Internal consistency and criterion validity of the SDS were investigated within an enriched community based sample of 577 Dutch frequent (≥ three days per week in the past 12 months) cannabis users between 18-30 years. Criterion validity was tested against the Composite International Diagnostic Interview (CIDI) 3.0 DSM-IV diagnosis cannabis dependence, and psychometric properties were assessed separately for males and females and for ethnic subgroups. Principal component analysis showed that all items of the scale loaded on a single factor and reliability of the SDS total score was good (Cronbach's α = 0.70). However, criterion validity against the CIDI diagnosis cannabis dependence was low: area under curve (AUC) was 0.68 (95% confidence interval: 0.64-0.73) and at the optimal differentiating cut-off (SDS ≥ 4), sensitivity was 61.3% and specificity 63.5%. Results were similar for subgroups on gender and ethnicity. While internal consistency of the SDS is good, its use as a screener to differentiate between dependence and non-dependence within populations of young adult frequent cannabis users is not recommended