Trauma Mental Health Screening Emergency Department Crowding Exposure and Post-Traumatic Stress Disorder Symptom Escalation Among Kenyan Survivors: A Target-Trial Emulation of Surge Thresholds

Emergency department crowding is a modifiable exposure that may amplify post-traumatic stress disorder (PTSD) symptoms among Kenyan injury survivors, yet the minimum crowding threshold at which screening and referral pathways degrade has not been formally characterised. No observational data were analysed. The analysis characterised the operating characteristics of the BACI estimator under a declared variance structure with between-cluster standard deviation of 6.0, residual standard deviation of 4.5, and intraclass correlation of 0.64. Power was estimated across 2000 replications per design cell for cluster counts of 8, 16, 24, 32 and effect sizes of 3, 5 and 8 percentage points. The analysis identified that 54 clusters are required to detect a 5-percentage-point effect at 80% power. The results indicate that the BACI design is feasible for crowding-threshold evaluations only at cluster counts substantially above those typical of single-county Kenyan hospital networks, and that effect sizes below 5 percentage points are unlikely to be detectable without multi-county sampling. Target-trial emulation of surge thresholds requires explicit power justification before data collection, and that the intraclass correlation of 0.64 imposes a design constraint that has been understated in prior trauma-screening implementation research.