Community Health Worker Caseload Spillovers and Mental Health Detection Sensitivity in Ethiopian Primary Care: A Boundary Discontinuity Design

Ethiopian primary care relies on community health workers whose caseloads are not confined to a single service domain, yet the standard evaluation of mental health detection treats caseload as a fixed attribute of the worker rather than a quantity that spills across the boundaries of the tasks a worker is assigned. No observational data are used or claimed. Under a declared variance structure with an intraclass correlation of 0.64, a between-cluster standard deviation of 6.0 and a residual standard deviation of 4.5, 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. The analysis identifies 54 clusters as the number required to detect a 5 percentage point effect at 80 per cent power, and it shows that the before-after-control-impact interaction is sensitive to the ratio of between-cluster to residual variance rather than to the absolute magnitude of either. The contribution is a design template and a set of power benchmarks that allow future field studies of caseload spillovers to be sized before they are funded, and a specification of the boundary conditions under which the design's estimates remain interpretable.