Municipal property-tax reassessment cycles and informal tenant turnover in Lagos local government areas: a difference-in-differences estimation of reassessment-timing thresholds

Municipal property-tax reassessment in Lagos local government areas is widely believed to accelerate informal tenant turnover, yet the timing thresholds at which such effects become detectable have not been formally characterised. 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 indicates that 54 clusters are required to detect a 5-percentage-point effect at 80 per cent power under the declared variance structure. Minimum detectable effect curves decline steeply between 8 and 24 clusters and flatten thereafter, implying that marginal returns to additional local government areas diminish once roughly two dozen clusters are enrolled. The contribution is a transferable design template for quasi-experimental evaluation of municipal fiscal timing in African urban settings, together with explicit boundary conditions under which the BACI estimator is and is not informative.