Convenience Voting Can Affect Election Outcomes

Forms of convenience voting, including voting-by-mail (VBM), provide citizens the opportunity to cast ballots without being exposed to the information revealed in the final weeks leading up to Election Day. This creates the possibility that informational differences will cause VBM and polling place voters to vote differently. We test this hypothesis by looking at whether the increased use of VBM at the precinct-level relates to candidates' vote shares in the 2008 California presidential primary. An election administration policy in California, in which all voters are assigned to VBM based on an arbitrary threshold of the number of registered voters, is exploited to overcome the identification problem caused by the self-selection of voters into VBM. We show that the use of VBM affects the relative performance of candidates remaining in the race and increases the probability of selecting withdrawn candidates. Our findings have implications both for election administration policy and for the study of campaign effects in American elections. Election officials should consider waiting until closer to Election Day to send out mail ballots, or instruct voters to wait until they are ready to make a decision before voting.