Patient outcomes and session dose in a randomized controlled trial of the Transdiagnostic Intervention for Sleep and Circadian Dysfunction: Influential factors and methodological considerations.
Milner A, Sarfan L, et al. • Behaviour research and therapy • 2026
Participants who completed the recommended number of TSC sessions showed larger effect sizes and more significant improvements relative to usual care, and Kaplan-Meier analyses established that eight sessions optimized outcomes for Standard TSC and six sessions for Adapted TSC.
Key Findings
Results
Completing the recommended number of TSC sessions was associated with larger effect sizes and more significant improvements compared to receiving a partial session dose.
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 sessions showed larger effect sizes relative to UC-DT compared to those who received only a partial session dose.
The comparison group was usual care followed by delayed treatment (UC-DT).
The primary outcome measured was sleep disturbance at post-treatment.
Results
The optimal session dose to improve the primary outcome of sleep disturbance at post-treatment was eight sessions for Standard TSC and six sessions for Adapted TSC.
Kaplan-Meier Survival Analyses were used to determine session thresholds.
Standard TSC required eight sessions to optimize the primary outcome of sleep disturbance at post-treatment.
Adapted TSC required six sessions to optimize the primary outcome of sleep disturbance at post-treatment.
These findings 'establish specific session thresholds for Standard and Adapted TSC to optimize clinical outcomes.'
Results
A substantial proportion of treatment dropouts showed meaningful clinical change by mid-treatment, though this did not differ significantly from completers.
20% of participants who dropped out of treatment showed a meaningful clinical change by mid-treatment.
This proportion did not differ significantly from the number of patients who received the full dose of treatment.
This finding suggests some participants may have achieved sufficient benefit before completing the full course of treatment.
Larger treatment effects were observed when assessments were completed within 3 months of their planned date.
Assessments completed outside this window were associated with smaller observed treatment effects.
This finding highlights the impact of methodological variations on treatment outcomes in implementation research.
Methods
The study examined an effectiveness-implementation hybrid trial design in which methodological variations such as session number, dropout, and assessment timing were systematically investigated.
The trial tested the Transdiagnostic Intervention for Sleep and Circadian Dysfunction (TSC) in both Adapted and Standard versions against UC-DT.
Total sample size was N = 539 adults with sleep and circadian problems.
Randomized controlled trial (RCT) methodology was used.
The study aimed to investigate 'variations that are not always systematically investigated' in RCTs assessing evidence-based psychological treatments.
What This Means
This research suggests that how many therapy sessions a person completes matters significantly when receiving a sleep-focused psychological treatment called the Transdiagnostic Intervention for Sleep and Circadian Dysfunction (TSC). In a large study of 539 adults with sleep and circadian problems, people who finished the full recommended course of treatment showed greater improvements in sleep disturbance compared to those who only completed part of the treatment or received usual care. The study also identified specific session thresholds: eight sessions for the Standard version of TSC and six sessions for the Adapted version appear to be the doses needed to achieve the best outcomes.
Interestingly, the study found that about 20% of people who dropped out of treatment still showed meaningful clinical improvement by the midpoint of therapy, though this rate was not statistically different from those who completed the full treatment. Additionally, the timing of outcome assessments mattered — when follow-up assessments were completed within three months of their scheduled date, larger treatment effects were detected, highlighting how logistical factors in research design can influence study results.
These findings matter because they provide practical guidance for clinicians and researchers implementing TSC in real-world settings. Knowing that six to eight sessions are needed to optimize outcomes can help therapists and patients set realistic expectations and plan accordingly. The results also underscore the importance of careful study design in clinical trials — factors like when assessments are conducted and how dropout is handled can meaningfully affect what conclusions are drawn about treatment effectiveness.
Milner A, Sarfan L, Diaz M, Esteva Hache R, Ovalle Patino E, Harvey A. (2026). Patient outcomes and session dose in a randomized controlled trial of the Transdiagnostic Intervention for Sleep and Circadian Dysfunction: Influential factors and methodological considerations.. Behaviour research and therapy. https://doi.org/10.1016/j.brat.2026.104987