Rural mobile-money agent density and informal savings-group dissolution in Ugandan sub-counties: an instrumental-variable estimation of proximity thresholds

The expansion of mobile-money agent networks across rural Uganda has been accompanied by the dissolution of rotating savings and credit associations (ROSCAs), yet the causal status of this association remains contested because agent placement is endogenous to local economic conditions. Because no observational data are analysed here, the paper characterises the operating characteristics of the proposed before-after-control-impact estimator under a declared variance structure: between-cluster standard deviation of 6.0, residual standard deviation of 4.5, and intraclass correlation of 0.64. Power was estimated across 2000 design cells spanning cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The design attains 80 per cent power at 54 clusters for a 5-percentage-point effect. The proximity threshold at which agent density begins to dissolve ROSCAs is identifiable only when the instrument's exclusion restriction is defended on institutional rather than statistical grounds, and it specifies the boundary conditions under which the estimator's operating characteristics remain credible. The contribution is a methodological one: a design that makes the dissolution mechanism estimable without conflating agent proximity with the demand shocks that jointly determine agent placement and group survival.