Voter mobilization efforts can depress turnout

We analyze the effects of a volunteer-led postcard writing campaign intended to turn out registered voters to support specific candidates in two state legislative districts. After adjusting for known selection bias in treatment assignment, we find that the postcards had a surprising negative effect on overall voter turnout. There is no evidence of effects being conditional on socioeconomic status or prior voting history. Of several explanations for this unexpected result, the most promising is that the focus on a down-ballot race distracted subjects from being aware of higher-profile contests on the ballot that might have motivated them to vote. We encourage researchers and practitioners to take negative findings seriously and develop tests for the explanations we offer.