Rural Cooperative Credit Access and Interdisciplinary Sociology Extension Uptake in Kenyan Arid Counties: A Regression Discontinuity Analysis of Savings-Group Eligibility Thresholds

Because no observational data are available, the study characterises the design's power to detect effects of 3, 5 and 8 percentage points across 8, 16, 24 and 32 clusters under a declared variance structure with an intraclass correlation of 0.64, between-cluster standard deviation of 6.0 and residual standard deviation of 4.5. Power was estimated across 2000 replications per design cell.54 clusters are required to detect a 5-percentage-point effect at 80% power, and that the minimum detectable effect declines steeply as cluster count rises from 8 to 32. The regression discontinuity design is feasible for evaluating savings-group thresholds only when the number of clusters exceeds the range typically available to single-programme evaluations in arid counties, and it derives the implications of this constraint for the design of interdisciplinary sociology extension evaluations.