Urban Sociology of Metropolitan Floodplain Building Permit Setback Variances and Informal Structure Demolition Notices in Accra's Drainage Corridor Wards: A Regression Discontinuity of Setback Thresholds

Building permit setback rules in Accra's drainage corridor wards create sharp administrative thresholds: structures inside the regulated setback are classified as informal and become eligible for demolition notice, while those just outside remain lawful. Because no observational data are available, the study characterises the operating characteristics of the design under a declared variance structure rather than estimating the threshold effect itself. A before-after-control-impact estimator was evaluated across 2000 replications per design cell, with cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The intraclass correlation was 0.64, between-cluster standard deviation 6.0 and residual standard deviation 4.5. Power curves, minimum detectable effect estimates and coefficient precision intervals were computed. The design achieved 80 per cent power at 5 percentage points only with 54 clusters, far exceeding the 8 to 32 clusters available in the corridor wards. The threshold design is underpowered at realistic cluster counts, that the minimum detectable effect at 32 clusters exceeds the plausible policy effect, and that the intraclass correlation of 0.64 is the binding constraint. The contribution is a design-based demonstration that regression discontinuity in clustered floodplain settings requires either cluster aggregation or within-cluster matching before threshold effects on demolition exposure can be identified.