2.1. Source of data

Data on treatment episodes were obtained for the years 2009, 2010, and 2011 from the Treatment Episode Dataset-Discharges (TEDS-D), a database of substance use treatment episodes in the United States. The TEDS is managed by the Substance Abuse and Mental Health Services Administration (SAMHSA) and includes information regarding admissions and discharges from treatment programs that receive public funding throughout the 50 U.S. States, the District of Columbia and Puerto Rico. This dataset includes information from the large majority of programs that provide treatment for substance use in the United States, but does not include data from settings that are entirely dependent on private revenue or, in most cases, treatment occurring in hospitals or correctional settings (SAMHSA, Center for Behavioral Health Statistics and Quality, 2016).

We limited our analyses to records from the TEDS in which clients had no prior treatment episodes so that each record represents a unique episode for a client. Furthermore, we removed all detoxification treatment episodes from the analysis as they are shorter and serve the purpose of stabilizing, not treating patients for substance use disorders. This approach is consistent with other studies that have removed detoxification episodes when evaluating factors associated with treatment completion in the TEDS (Saloner et al., 2014; Sahker et al., 2015). For the sake of completeness, sensitivity analyses were conducted including detoxification episodes and this had no effect on results of the analyses (results not shown). Analyses were also limited to those who presented to treatment primarily for problems related to alcohol, cannabis, stimulants and opioids; treatments for other substances made up only 2% of treatment episodes and were excluded. Finally, we excluded eight states that did not report the psychiatric comorbidity variable to TEDS: Connecticut, Georgia, Minnesota, Oregon, Texas, Vermont, Virginia, and Nevada, and a ninth state as an extreme outlier, Michigan, which only reported 0.31% treatment episodes as having a psychiatric comorbidity.