The Drug Abuse Treatment Outcome Studies (DATOS) were initiated in 1989 under contracts funded by the National Institute on Drug Abuse (NIDA) to evaluate drug abuse treatment outcomes and emerging treatment issues in the United States. This was NIDA's third national outcome evaluation study of publicly funded treatment. The research plan for the adult component of DATOS was based on studies and findings about drug abuse treatment outcomes over the past 30 years. Much of this knowledge came from previous national, multisite longitudinal evaluation studies funded by NIDA. The two previous studies—the Drug Abuse Reporting Program (DARP) and the Treatment Outcomes Prospective Study (TOPS)—helped shape the direction and research questions for the DATOS of treatment outcomes and drug abuse patterns. The companion adolescent study began ...