title: Temporal and gender trends in concordance of urine drug screens and self-reported use in cocaine treatment studies.
abstract: OBJECTIVE
  To describe temporal trends in concordance, sensitivity, and specificity and to explore demographic trends in concordance in two outpatient treatment studies for cocaine dependence.
  
  
  METHODS
  We obtained 2229 urine drug screens from 129 individuals, along with accompanying self-use reports. Paired self-use reports and urine drug screens were considered concordant if the two measures of cocaine use were in agreement. The sensitivity and specificity of the self-use reports in predicting the urine drug screen 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
  Over the course of our studies, both sensitivity and concordance statistically decreased, yet specificity remained relatively constant. Median concordance for all subjects was 88%. Among all subjects, concordance varied significantly by gender, with females achieving significantly higher concordance than males (96% vs. 86%). Similarly, females were almost twice as likely to achieve 100% concordance as males (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 self-use reports 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.
authors.affiliation: Department of Biostatistics, Bioinformatics and Epidemiology Medical University of South Carolina 135 Cannon Street Suite 303 Charleston, SC 29425.
authors.forename: Megan S
authors.initials: MS
authors.lastname: Schuler
authors.forename: William V
authors.initials: WV
authors.lastname: Lechner
authors.forename: Rickey E
authors.initials: RE
authors.lastname: Carter
authors.forename: Robert
authors.initials: R
authors.lastname: Malcolm