Where does corruption risk sit? Core–periphery structure and clustering of single bidding in Ecuador’s subnational public procurement networks

Abstract Single bidding, the award of a competitive tender that attracted only one offer, has become a widely used proxy for corruption risk in public procurement. Recent work on European Union markets showed that this risk concentrates in the core of some national procurement networks and in the periphery of others, and that it clusters in groups of buyers and suppliers. This study tests whether these regularities hold at the subnational scale of a Latin American country. Using Open Contracting Data Standard records from Ecuador’s National Public Procurement Service, it analyses 46,279 contracts awarded through competitive procedures between 2015 and 2021, linking 2,838 public buyers and 15,856 suppliers. Buyer–supplier networks were built nationally by year and for 21 provinces. A strength-based k-shell decomposition identified market cores, and edge communities were detected on line graphs. Both measures were compared with null models that shuffle single-bid labels within product categories. Single bidding affected 30.2% of procedures and ranged from 20% to 44% across provinces. It was significantly clustered in every national network and in 17 of 21 provinces, at 1.2 to 2.0 times the null expectation. Unlike the cross-country European pattern, the size of the market core was unrelated to provincial risk (r = − 0.19). Provinces with more single bidding were instead those where single bidding concentrated in the core (r = 0.53, p = 0.014). The results suggest that subnational procurement markets organise risk in different ways and that audits could prioritise central actors where this concentration is detected.