Incumbency and campaign spending are key determinants of electoral success in legislative elections. In open-list proportional representation systems, their impact might be contingent on the number of open seats in each district. When there are more open seats, incumbents seeking re-election and those who spend more should have higher chances of success. Using data from 2216 candidates in the 2017 and 2021 Chamber of Deputies elections in Chile’s 28 districts, we assess the presence of the mediating effect of open seats. We confirm the importance of incumbency and campaign spending, but the interaction effects of open seats with incumbency and campaign spending are not significant for the chances of winning a seat. The presence of open seats might induce more competitive challengers to enter the race, diluting the expected positive interaction of open seats with incumbency and campaign spending on electoral success.
Martínez et al. (Fri,) studied this question.