Urban Development Sociology of Municipal Bus Rapid Transit Fare-Zone Boundary Rules and Informal Minibus Operator Route Exit in Kenyan Cities: A Regression Discontinuity Analysis of Fare Thresholds

Municipal bus rapid transit schemes in Kenyan cities set fare-zone boundaries that alter the operating economics of informal minibus routes. Whether these boundaries cause minibus operators to exit particular corridors is a question that regression discontinuity designs are well suited to answer, yet the credibility of any such design depends on statistical power that has not been characterised for the clustered corridor structure of Kenyan urban transport. The analysis used a between-cluster standard deviation of 6.0, a residual standard deviation of 4.5, and an intraclass correlation of 0.64, with 2000 replications per design cell across cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. Power was estimated for the interaction between fare-zone boundary exposure and route exit. The design required 52 clusters to detect a 5 percentage point effect at 80 per cent power. The intraclass correlation of 0.64 imposes a cluster-count floor that most single-city evaluations cannot meet, and that the fare-zone discontinuity should therefore be analysed as a multi-city comparative design rather than a within-city natural experiment. The framework specifies the estimand, the identifying assumptions, the clustering structure and the reporting standards that a credible regression discontinuity study of fare-zone boundaries would require.