Urban development fee decentralization and informal enterprise registration in Freetown wards: a difference-in-differences estimation of municipal revenue-autonomy thresholds

Municipal fee decentralization in Freetown has been promoted as a route to both revenue autonomy and the formalization of informal enterprises, but the ward-level evaluations meant to test that claim are fragile in ways that are rarely made explicit. Under a declared variance structure with a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5 and an intraclass correlation of 0.640, power was estimated across 2000 replications per design cell. The BACI interaction detects a five-percentage-point effect at eighty per cent power only when fifty-four wards are enrolled, a figure well above the eight to thirty-two wards that Freetown's current ward structure and typical evaluation budgets make available. Minimum detectable effects at the smaller cluster counts exceed the plausible policy effect, so that null results in such evaluations cannot be read as evidence of decentralization failure. The contribution is a design-diagnostic for revenue-autonomy research: it specifies the cluster counts at which BACI estimation becomes informative and identifies the intraclass correlation as the binding constraint on inference.