Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
We develop and test a theory of voting and turnout decisions that integrates self-interest, social preferences, and expressive motives. Our empirical analysis studies referenda among university students about whether to collectively purchase deeply discounted flat rate tickets for public transportation and cultural amenities. Individual usage data allow quantifying the monetary benefits associated with each ticket. We find that monetary benefits strongly influence participation and voting. However, social or expressive motives such as stated altruism are decisive for a significant minority. Based on our theory, empirical results rule out purely expressive voting.