To describe temporal trends in concordance, sensitivity, and specificity and to explore demographic trends in concordance in 2 outpatient treatment studies for cocaine dependence.
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.
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.
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: email@example.com.
Supported by National Institute on Drug Abuse grants R01 DA019903 and R01 DA016368.