Patient Outcomes and Session Dose in a Randomized Controlled Trial of the Transdiagnostic Intervention for Sleep and Circadian Dysfunction: Influential Factors and Methodological Considerations

Randomized controlled trials (RCTs) assessing the implementation of Evidence-based psychological treatments (EBPTs) into clinical practice may involve variations that are not always systematically investigated. This study aimed to investigate the impact of such variations in the context of an effectiveness-implementation hybrid trial - specifically, the relationship between trial outcomes and number of treatment sessions, dropout, and differences in assessment timing. Adults ( N = 539) with sleep and circadian problems were randomized to TSC (Adapted or Standard version) or usual care followed by delayed treatment (UC-DT). Participants who completed the recommended number of TSC sessions showed larger effect sizes and more significant improvements relative to UC-DT, when compared to participants who received a partial session dose. Notably, a substantial number of participants who dropped out of treatment showed a meaningful clinical change by mid-treatment (20%), though this number did not differ significantly from the number of patients who remained in treatment. Larger treatment effects were observed when assessments were completed within 3 months of their planned date. Kaplan-Meier Survival Analyses indicated that the dose to optimize the primary outcome of sleep disturbance at post-treatment was eight sessions for Standard TSC and six sessions for Adapted TSC. This study underscores the potential impact of methodological variations on the implementation of TSC into clinical practice, particularly in relation to dose and assessment timing. These findings have important implications, such as offering support for methodological steps to ensure that these variables are routinely monitored and/or included. • This study highlights the importance of methodological considerations when assessing randomized controlled trials of the implementation of psychological treatments into clinical practice. • Results showed that completing the recommended course of treatment resulted in greater improvements, and treatment benefits were largest when follow-up assessments were conducted promptly. • However, significant improvements were still observed despite these methodological deviations, suggesting that there is room for flexibility, allowing clinicians to adapt treatment based on patient progress.