study may have yielded lower rates of use than self-administered questionnaires or computer-assisted self-interviews (Turner et al. 1998; Wright et al. 1998). Furthermore, although self-reports of substance use obtained in the context of good rapport, privacy and with the assurance of confidentiality are generally valid (Brener et al. 2003; Harrell 1997; Winters et al. 2008), biological procedures could be incorporated into future work to provide additional information about the accuracy of adolescent reports (Wagenaar et al. 1993).
