Objectives: To describe temporal trends in concordance, sensitivity, and specificity and to explore demographic trends in concordance in 2 outpatient treatment studies for cocaine dependence.
Methods: We obtained 2229 urine drug screens (UDS) from 129 individuals, along with accompanying self-use reports (SUR). Paired SUR and UDS were considered concordant if the 2 measures of cocaine use were in agreement. The sensitivity and specificity of the SUR in predicting the UDS was also estimated. To model concordance, sensitivity, and specificity as a function of time, generalized estimating equations were used. Demographic effects on concordance among subjects who achieved 100% concordance and subjects who achieved a recently proposed 70% concordance threshold were tested.
Results: During the course of our studies, both sensitivity and concordance statistically decreased; however, specificity remained relatively constant. Median concordance for all subjects was 88%. Among all subjects, concordance varied significantly by gender, with women achieving significantly higher concordance than men (96% vs 86%). Similarly, women were almost twice as likely to achieve 100% concordance as men (42% vs 22%). Finally, 80% of participants achieved the 70% concordance threshold, and no differences among demographic groups with regards to the 70% concordance threshold were observed.
Conclusions: Temporal effects of concordance and sensitivity may have profound repercussions when using SUR to gauge efficacy of an experimental intervention. Furthermore, gender may differentially affect concordance. Finally, a substance abuse outcome measure that reliably combines objective and self-report data is promising, but further research is needed.
From the Department of Biostatistics, Bioinformatics and Epidemiology (MSS, REC), Medical University of South Carolina, Charleston, SC; and Center for Drug and Alcohol Programs (WVL, RM), Medical University of South Carolina, Charleston, SC.
Received for publication September 2, 2008; accepted February 12, 2009.
Send correspondence and reprint requests to Megan S. Schuler, BS, Johns Hopkins Bloomberg School of Public Health, Department of Mental Health, Baltimore, MD, 21215. E-mail: firstname.lastname@example.org.
Supported by National Institute on Drug Abuse grants R01 DA019903 and R01 DA016368.