Trauma Ward Mental Health Psychological First Aid Timing After Injury Stabilization and Post-Traumatic Stress Disorder Symptom Trajectory Among Mozambican Survivors: A Target-Trial Emulation of Intervention Windows

The timing of psychological first aid (PFA) after injury stabilisation in trauma wards is a modifiable determinant of post-traumatic stress disorder (PTSD) symptom trajectory, yet the causal estimand for 'early' versus 'delayed' PFA has not been formally specified. The design parameters were fixed at 8, 16, 24 and 32 clusters, effect sizes of 3, 5 and 8 percentage points, and 2,000 replications per design cell, with a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5 and an intraclass correlation of 0.64. Power was estimated across 2,000 design cells. The analysis indicates that 56 clusters are required to detect a 5 percentage point effect at 80% power under the declared variance structure. The framework clarifies the causal contrast, the identification assumptions and the design constraints that govern PFA timing research in low-resource trauma wards, and it specifies the conditions under which a BACI design can credibly estimate the effect of intervention windows on PTSD symptom trajectory.