Rural Development Interdisciplinary Sociology of Water User Association Audit Exposure and Irrigation Fee Arrears in Tanzanian Smallholder Schemes: A Difference-in-Differences Analysis of Audit Publication Timing

Water user associations in Tanzanian smallholder irrigation schemes are increasingly subject to externally conducted financial audits whose publication timing varies across districts, creating a natural policy discontinuity that researchers have proposed to exploit through before–after–control–impact (BACI) designs. The credibility of such evaluations depends on the operating characteristics of the BACI interaction estimator under realistic clustering of irrigation fee arrears within schemes, yet those characteristics have not been systematically 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 reduction in arrears at 80% power, a requirement that exceeds the cluster counts typically available in district-level audit rollouts. Minimum detectable effects at 80% power remain above 5 percentage points for all cluster counts examined. The results imply that BACI evaluations of audit timing in this setting are underpowered at feasible cluster counts, and that the intraclass correlation of 0.64 dominates the design's sensitivity.