We assessed substance problem severity with three sets of variables from the baseline interview. First, type of substance dependence was based on questions from the Diagnostic Interview Schedule for Psychoactive Substance Dependence to provide a DSM-IV diagnosis for alcohol, marijuana, stimulant, painkiller, methadone, heroin, barbiturate, tranquilizer, inhalant, hallucinogen, and cocaine dependence and abuse (American Psychiatric Association, 2000). For each substance, we established presence or absence of three of seven dependence symptoms (or one of three abuse symptoms) during the previous 6 months (Mertens and Weisner, 2000; Weisner et al., 2000, 2001a), and then categorized respondents as having alcohol-only, drug-only, or alcohol and drug dependence, or abuse only (no dependence). Secondly, we measured severity of substance use and related problems at baseline with the alcohol, drug, medical, social, psychiatric, legal and employment composite scores of the Addiction Severity Index (ASI) instrument (McLellan et al., 1992). Composite scores ranged from zero (no problems in the relevant domain) to 1.0 (high severity). We included number of years of regular use based on self-report, recorded at baseline, for alcohol, pain killers, marijuana, stimulants and
