Police Custody Trauma Exposure and Mental Health Crisis Presentation in Nigerian Detention Facilities: An Instrumental-Variable Analysis of Pretrial Detention Duration

Pretrial detention in Nigerian custody facilities exposes detainees to trauma and is associated with mental health crisis presentation, but the causal effect of detention duration is confounded by offence severity and facility assignment. The analysis is a design and power evaluation, not an empirical estimate: no observational data are used or claimed. Under a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5 and an intraclass correlation of 0.64, the design was evaluated across 2000 replications per cell for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. Power rose with cluster count and effect size, and 54 clusters were required to detect a 5-percentage-point effect at 80% power. Docket randomisation is a defensible identification strategy for detention-duration effects, but that the intraclass correlation of 0.64 imposes a cluster-count floor that most single-state Nigerian studies cannot meet. The contribution is a design template and a power benchmark for future custody-trauma research, not a causal claim about Nigerian detainees.