substances they have heard of and only asked about substance consequences if they have actually used the drug; see Table 1 for gating details for each instrument). Because youth may enter the study with some prior substance use, the baseline battery measures lifetime patterns of substance use [including whether they used a substance, age of first- and regular-use assessment, total lifetime quantity (in standard units), maximum lifetime dose, and length of abstinence] of all major drug categories (see section C.1c below for details within each drug category) (Johnston et al., 2017). Next, recent low level use (first sip of alcohol, first puff of cannabis or nicotine) and detailed 6-month quantity and frequency data for each of the aforementioned substance categories are assessed with a computerized modified Timeline Followback interview (TLFB) (Sobell and Sobell, 1996; Robinson et al., 2014). For the measures assessing substance use patterns among youth actually endorsing using a drug, visual aids are provided to improve accuracy of dosing, product identification, and routes of administration. In subsequent waves, the TLFB interview will be utilized to cover measurement of substance use patterns across all ten years to ensure continuous coverage. After the patterns of use are assessed, measures related
