Screening for Bid Rigging—Does It Work?

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This paper proposes a method to detect bid rigging by applying mutually reinforcing screens to a road construction procurement dataset from Switzerland in which no prior information about collusion was available. The screening method is particularly suited to address the problem of partial collusion, that is, collusion that does not involve all firms and/or all contracts in a specific dataset, implying that many of the classical markers discussed in the corresponding literature will fail to identify bid rigging. In addition to presenting new screens for collusion, it is shown how benchmarks and the combination of different screens may be used to identify subsets of suspicious contracts and firms. The discussed screening method succeeds in isolating a group of “suspicious” firms exhibiting the characteristics of a local bid-rigging cartel with cover bids and a—more or less pronounced—bid rotation scheme. Based on these findings, the Swiss Competition Commission (COMCO) opened an investigation and sanctioned the identified “suspicious” firms for bid rigging in 2016.