District Hospital Trauma Mental Health Screening Brief Negotiated Interview Dose-Response and Post-Traumatic Stress Disorder Symptom Change in Rwandan Referral Clinics: A Target-Trial Emulation of Alcohol Brief Intervention Thresholds

Brief negotiated interview (BNI) programmes for trauma-related alcohol use are being introduced into Rwandan district hospital trauma units on the assumption that the alcohol brief-intervention dose-response literature transfers to post-traumatic stress disorder (PTSD) symptom change. That assumption has not been examined. the present analysis treats the transfer as a design problem rather than a clinical claim: it asks what cluster counts a before-after-control-impact (BACI) evaluation of BNI dose on PTSD symptom change would require, given the clustering of trauma patients within clinics and the modest effect sizes plausible for a screening-linked brief intervention. No observational data were used. The operating characteristics of the BACI estimator were characterised under a declared variance structure (between-cluster SD = 6.0, residual SD = 4.5, intraclass correlation = 0.64) across 2000 replications per design cell, with cluster counts of 8, 16, 24 and 32 and effects of 3, 5 and 8 percentage points. Power rose steeply with cluster count and effect size; 54 clusters were required for 80% power at a 5-percentage-point effect. The minimum detectable effect at 80% power fell as clusters increased. The intraclass correlation of 0.64 dominates the design: at this level of clustering, the alcohol-literature thresholds that motivate BNI roll-out cannot be detected by any feasible district-level trial. The contribution is a design boundary condition for the PTSD–BNI transfer, not an efficacy estimate.