Community Mental Health Services Task-Shifting to Lay Counsellors and Diagnostic Boundary Erosion in Zambian Primary Care: A Multilevel Variance Decomposition

Task-shifting mental health services to lay counsellors in Zambian primary care has been promoted as a pragmatic response to specialist shortages, yet the diagnostic consequences of this workforce substitution remain poorly specified. Using a conceptual model grounded in the boundary-work tradition and implementation science, the analysis specifies the variance components that a multilevel design would estimate and the conditions under which diagnostic boundary erosion—the widening of symptom categories beyond their intended scope—would be expected to concentrate at particular levels. The framework proposes that counsellor-level factors, particularly supervision intensity and training duration, account for a substantial share of between-counsellor variance in diagnostic assignment, while facility-level factors contribute a smaller but non-trivial share through referral pathways and record-keeping practices. Variance decomposition offers a more precise diagnostic for boundary erosion than aggregate concordance statistics, because it locates the phenomenon at the level where intervention is feasible. The contribution is a specification of the multilevel structure of diagnostic boundary erosion under task-shifting, together with the design parameters and reporting standards that would permit empirical estimation in Zambian primary care settings.