In this analysis of how electoral rules and outcomes shape the internal organization of political parties, we make an analogy to primary elections to argue that parties use preference-vote tallies to identify popular politicians and promote them to positions of power. We document this behavior among parties in Sweden's semi-open-list system and in Brazil's open-list system. To identify a causal impact of preference votes, we exploit a regression discontinuity design around the threshold of winning the most preference votes on a party list. In our main case, Sweden, these narrow “primary winners” are at least 50% more likely to become local party leaders than their runners-up. Across individual politicians, the primary effect is present only for politicians who hold the first few positions on the list and when the preference-vote winner and runner-up have similar competence levels. Across party groups, the primary effect is the strongest in unthreatened governing parties.
Folke, Olle, Torsten Persson and Johanna Rickne (2016),
"The Primary Effect: Preference Votes and Political Promotions".
American Political Science Review