Does Unequal Representation Bias Policymaking? Quasi‐Experimental Evidence From the Italian Senate

How does unequal representation affect policymaking? Existing research shows that overrepresented districts exert disproportionate influence over public policy, yet our understanding of the underlying sources of this advantage remains limited. I argue that increased representation can independently bias policymaking via two channels: a mechanical effect, whereby additional representatives increase a district's likelihood of shaping the legislative agenda, and a behavioral effect, whereby legislators intensify constituency‐oriented effort due to intra‐district competition. To test this, I leverage the quasi‐experimental setting created by the electoral rule of the Italian Senate (1994–2006), which allowed districts with similar population sizes to elect either one or two senators. Using a regression discontinuity design and comprehensive data on bill (co‐)sponsorship, I find evidence consistent with both channels. Examining policy outcomes, I do not find that unequal representation yields distributive benefits, but I do find suggestive evidence of a broader legislative advantage.