Self-report measures are, by far, the most commonly used method of gathering information about substance use. Compared with toxicology screens and collateral reports, self-report measures are cheap, easy to administer, and widely accessible. In addition, when taken voluntarily and with assurances of confidentiality, self reports have been shown to produce valid inferences concerning substance use and abuse (Babor, Stein-berg, Anton, & Del Boca, 2000; Basurto et al., 2009). In fact, a number of researchers have suggested that biochemical and collateral data contribute little unique information above and beyond the information obtained from properly collected self-report measures (Laforge, Borsari, & Baer, 2005; Babor et al, 2000