At baseline, a 6-months web-based modified Timeline Followback (TLFB) is administered (developed by the first author and Dr. Bartsch). Consistent with the original TLFB (Sobell and Sobell, 1996; Robinson et al., 2014), the ABCD TLFB uses a calendar-based interviewer-administered retrospective report of detailed quantity/frequency substance use patterns during the past 6 months. The TLFB is a psychometrically sound instrument used to measure both alcohol and other drugs (Sobell and Sobell, 1996) (including cannabis, nicotine, cocaine), demonstrating reliability and validity for intervals up to 1 year (360 days) in adolescents and adults (Robinson et al., 2014; Fals-Stewart et al., 2000). For example, reliability indices are high for measuring cannabis use in the past year, including total joints used (0.95), greatest number of joints on any day (.93), and number of joints used per using day (0.94) (Robinson et al., 2014). As with the original TLFB, the ABCD TLFB utilizes memory cues, such as holidays and personal events elicited from the youth that may improve substance use recall (e.g., sleepovers, birthdays, parties, holidays) and these are populated onto the web-based calendar. The
