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We evaluate whether an econometric technique that is used in the spatial econometrics and network effects literature can be adopted as a test for collusive bidding in public procurement auctions. The proposed method is applied to the Swedish asphalt cartel that was discovered in 2001. Our dataset covers the period 1995–2009, which makes it possible to test for conditional independence between complementary cartel bids before and after 2001. Our estimates show a significant positive correlation between complementary cartel bids during the cartel period, whereas a non-significant correlation is shown during the later period. The variance of the parameter estimate of interest also differs between the periods, which suggests a structural change in bidding behavior among cartel members between the two periods.