Experimental Design
We first identify municipalities with an active bidding ring presence. We then send out letters to municipal legislators and government officials informing them of this fact. We split our sample of municipalities into the treatment and control groups using rerandomization. The variables that we use for rerandomization are the log number of total contracts let by the municipality, the value of the estimated RD coefficients, the p-values of the RD estimates, and the municipal vote shares of the Liberal Democratic Party in the July 2022 House of Councilors election. We use the Mahalanobis distance to test for balance of the covariates.