Police unit composition and extrajudicial killing complaints in Kenya: a difference-in-differences evaluation of ethnic-balance reforms and accountability outcomes

Kenya's ethnic-balance reforms to police unit composition were intended to reduce extrajudicial killings by aligning police demographics with the communities they serve. the present analysis evaluates the design logic of that reform using a difference-in-differences framework. Because no observational data are available, the study characterises the operating characteristics of the before-after-control-impact estimator under a declared variance structure: 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 and 32 and effect sizes of 3, 5 and 8 percentage points.54 clusters are required to detect a 5-percentage-point reduction in extrajudicial killing complaints at 80% power. The results indicate that the ethnic-balance reform's accountability mechanism is statistically detectable only at cluster counts substantially larger than Kenya's current police divisional structure provides. The reform's theory of change is plausible but that its evaluation architecture is underpowered, and it derives the cluster thresholds at which credible accountability claims become possible.