Incumbency advantage in multi-member districts: Evidence from congressional elections in Chile

• Holding 2 seats as opposed to holding only one grants an extra 4.5% vote share and increases by 28% the probability of electing 2 candidates again.
• Incumbency advantage estimates are similar to those obtained in previous studies in the U.S.
• Estimates, however, contrast with results obtained in other developing countries, which find a negative advantage to incumbency.

Do parties enjoy an advantage to incumbency in multi-member districts? In this paper we answer this question by adapting a regression-discontinuity design to multi-member districts in congressional elections in Chile. The electoral system in place generates discontinuities in the number of elected representatives from each coalition at the 1/3 and 2/3 thresholds of the two-party vote share. Regression-discontinuity estimates indicate that, by holding two seats as opposed to holding only one, the left-leaning coalition obtains an extra 4.5% vote share in the next election and increases by 28 percentage points the probability of electing two candidates again. These results are in line with those obtained in previous studies in the U.S. but contrast with results obtained in developing countries which find a negative advantage to incumbency.