Assessment concordance and predictive validity of self-report and biological assay of cocaine use in treatment trials.

ABSTRACT

BACKGROUND AND OBJECTIVES: Cocaine use during randomized clinical trials (RCTs) is typically assessed by participant self-report or biological assay (eg, urinalysis). There have been few direct comparisons of these assessment methods to investigate their concordance and their predictive validity for cocaine use and psychosocial outcomes following treatment completion. METHOD: In a combined sample of 380 participants from 5 cocaine RCTs, the concordance between cocaine use assessment methods was examined. Sequential multiple linear and logistic regression models evaluated the predictive validity of two assessment methods for cocaine use and psychosocial outcomes assessed at 1, 3, 6, and 12 months after treatment. RESULTS: Concordance for self-report and urinalysis indicators of cocaine use was high within-treatment (k = 0.72) and moderate during follow-up (k = 0.51). Rates of concordance were higher in studies using test cups with immediate urinalysis results. Regression analyses indicated that self-report data within-treatment predicted self-reported cocaine use at all post-treatment points (ß 0.22-0.30, p < .01), while urinalysis results within-treatment predicted urinalysis results at 1, 3, and 6 months post-treatment (OR 3.92-20.99, p < .05). Cocaine-positive urinalyses within-treatment were negatively associated with a composite "good outcome" indicator at 1 and 3 months post-treatment (OR 0.17-0.32, p < .05). DISCUSSION AND CONCLUSIONS: These results suggest a significant role of method variance in predicting post-treatment outcomes from within-treatment cocaine use indices. SCIENTIFIC SIGNIFICANCE: Results support recommendations that cocaine treatment trials should include both biological assay and self-report assessment. Test cups may facilitate increased self-report accuracy.