Substance use was assessed at the 4-month follow-up using the Alcohol and Drug Timeline Follow-back Interviews (TLFB; Sobell & Sobell, 1996). To maximize our observation window, we selected the version that assesses days of alcohol or drug use over the previous 3 months. TLFB measures have been widely used and are generally found to be reliable (Fals-Stewart, O’Farrell, Freitas, McFarlin, & Rutigliano, 2000). To obtain some indication of the reliability of the TLFB self-report, 58 participants provided saliva samples at follow-up that were tested by LabOne for cocaine, amphetamines, marijuana, opiates, and phencyclidine. Of the 13 participants reporting drug use within the last 30 days, 31% showed a positive objective screen. Conversely, of the 45 who denied drug use, two individuals (4%, one from each condition) showed a positive objective screen. These results provide some limited objective support for the validity of the self-reports.
