Opinion polls and other surveys are used to capture public sentiments on a variety of issues. If citizens are unwilling to reveal certain policy preferences to others, surveys may fail to characterize population preferences accurately. The innovation of this paper is to use unique data that allow one to measure biases in surveyed preferences for a broad range of public policies. I combine data on 184 referenda held in Switzerland between 1987 and 2007 with postballot surveys that ask how the citizens voted for each proposal. The difference between stated preferences in the survey and revealed preferences at the ballot box provides a direct measure of survey bias. I find that these biases vary by policy area, with the largest occurring in policies on immigration, international integration, and votes involving liberal or conservative attitudes. Also, citizens show a tendency to respond in accordance with the majority.