The Contribution of Treatment Allocation Method to Outcomes in Intervention Research

The purpose of this methodological study was to examine the contribution of treatment allocation method (random vs. preference) on the immediate, intermediate, and ultimate outcomes of a behavioural intervention (MCI) for insomnia. Participants were allocated to the MCI randomly or by preference. Outcomes were assessed before, during, and after completion of the MCI using validated self-report measures. Analysis of covariance was used to compare the post-test outcomes for the 2 groups, controlling for baseline differences. Compared to those randomized, participants in the preference group showed improvement in most immediate outcomes (sleep onset latency, wake after sleep onset, sleep efficiency), both intermediate outcomes (insomnia severity and daytime fatigue), and one ultimate outcome (resolution of insomnia). Using a systematic method for eliciting participants' preferences and involving participants in treatment selection had a beneficial impact on immediate and intermediate outcomes. Additional research should validate the mechanism through which treatment preferences contribute to outcomes.