Keywords: political competition, electoral systems, corruption.
The economic and political literature widely studied the effects of electoral system
on corruption. But very little attention has been dedicated to the role of political competition
in explaining this relationship. We hypothesize that the proportionality degree of the
electoral system impacts corruption directly and in a conditional way: through the degree of
electoral competition among political parties. The estimation results, on a sample of the 20
Italian regions over 26 years, show that both the direct and the indirect effect matter in explaining
corruption. As the electoral system becomes more proportional, corruption directly
decrease. This beneficial effect can be reinforced or depressed depending on how political
competition reacts to changes in the proportionality degree of the electoral system.