Does the top two primary system moderate the voting behavior of elected officials?

Objective: Top two primary systems have been touted to increase moderation in politics. In a top two primary, the two candidates with the most votes continue on to the general election even if they are from the same political party. Candidates no longer have to cater to the extremes of their party in order to make it through the primary, so the thought is that candidates would be encouraged to be moderate throughout the election cycle to attract the median voter. Methods: Washington State adopted a top two primary system in 2008, which allows us to look at empirical evidence about whether the top two primary actually encourages moderation in politics. We analyze voting records of elected officials before and after the adoption of the top two primary. Results: We find evidence that the top two primary correlates with moderation in the voting behavior of elected officials, ceteris paribus. Conclusion: Policymakers may want to consider the structure of primaries and how they could be changed to help encourage moderation in the voting of elected officials.