Indigenous Age-Set Solidarity and Informal Insurance Crowd-Out in Igbo Rotating Savings Associations: A Lab-in-the-Field Experiment on Mutual-Aid Norms and Risk Pooling

The central problem is that indigenous mutual-aid obligations may function as a substitute for market-based risk-pooling instruments, yet the mechanism by which normative obligation displaces insurance uptake remains under-theorised. The design uses a before-after-control-impact estimator to characterise the operating characteristics of the proposed experiment under a declared variance structure with an intraclass correlation of 0.64, between-cluster standard deviation of 6.0 and residual standard deviation of 4.5. Power was estimated across 2000 design cells for cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The analysis indicates that 54 clusters are required to detect a 5-percentage-point effect at 80 per cent power. The contribution is a methodological framework that specifies the conditions under which normative obligation can be distinguished from material self-interest in insurance decisions, and a set of derived propositions about the boundary conditions of crowd-out in indigenous risk-sharing institutions.