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When the Study Population isn't Like the Target Population, Do the Results Still Apply?

Although there are a number of effective evidence-based interventions for substance use disorders (SUDs), strong stigma toward these conditions and limited access to treatment often prevent many people with SUDs from receiving effective treatment.

Web-based SUD treatment is a promising behavioral intervention for treating individuals who may not be willing or able to receive traditional face-to-face interventions.

A number of randomized controlled trials (RCTs) have found web-based interventions to be effective in treating SUDs and increasing retention, however, these study results do not necessarily guarantee effectiveness for the interventions for different populations. This is particularly true when the characteristics of the study participants are different from the target population, those who will actually be using the intervention.

In order to see if the results of a CTN evaluation of a web-based intervention, the Therapeutic Education System (TES), were generalizable to treatment-seeking adults, this study used a selection model approach to make the original study sample more closely resemble the target population.

The study sample (n=507) was compared with a target population of SUD treatment-seeking adults taken from the Treatment Episodes Data Set-Admissions (TEDS-A), an administrative database maintained by SAMHSA that includes annual data on more than 1.5 million admissions to publicly-funded SUD treatment facilities across the U.S.

Analyses revealed substantial differences between the study sample and the target population. The study sample had significantly lower proportions of individuals with intravenous drug use or a history of prior SUD treatment. It also had significantly higher proportions of individuals with 12 years or more educational attainment and  full-time jobs.

Weighting the original study sample to make it more closely resemble the target population and then comparing effect sizes of the unweighted and weighted models revealed no significant treatment effects on abstinence at 12 weeks and 6 months ‚ÄĒ very different results from the original study. Treatment effects on retention were insignificant for both weighted and unweighted analyses.

Conclusions: This study demonstrated significant differences between the study sample of a web-based SUD intervention and the target population of potential recipients of that intervention. This study also demonstrated that the observed promising findings of the original TES study (CTN-0044) may not be directly applicable to the potential target population. Given the great potential for scalability of web-based SUD interventions, the representativeness of a study sample with regard to the target population of potential users for this intervention should be carefully considered. 

Citation: Susukida R, et al. Generalizability of the Findings from a Randomized Controlled Trial of a Web-Based Substance Use Disorder Intervention. American Journal on Addictions 2018 (in press).

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