Abstract: Voters often lack sufficient knowledge to make educated decisions. We investigated how a decision aid-–the Information and Choice Questionnaire (ICQ)—helped them make more consistent decisions. The ICQ is designed for large-scale use and provides voters with information about a specific problem before asking them for their opinions. It provides citizens with information summarizing a full range of viable policy options and the probable consequences of each, as provided by experts. We investigated the ICQ in the context of the Dutch 2005 referendum on the European Constitutional Treaty. Respondents (N = 340) constituted a random sample of the Dutch population. We studied the effects of the ICQ on vote preferences and the consistency of voters’ preferences shortly before the referendum. We were especially interested in the moderating role of political sophistication on the uses and effects of the ICQ. Our study confirmed that many voters had little knowledge about the European Constitution and had inconsistent preferences. The ICQ made their vote preferences more consistent, especially for those participants with lower levels of political sophistication. This suggests that this decision aid can narrow the gap between the politically sophisticated and the politically less sophisticated.