How do political parties determine their platform? To answer this question the literature either relies on observational data or scholars use theoretical models to investigate party behavior. On the one hand empirical studies usually cannot uncover the causal mechanisms which underlie observed patterns in party platform change, on the other hand theoretical models rest on strong assumptions about the rationality of political decision makers. Recent studies have demonstrated that humans deviate in a consistent manner from rational behavior, namely that decisions depend on a reference point. However, what that reference point exactly entails is still under-theorized. By comparing the predictions of game-theoretical models with those of prospect theory in an experiment in which parties compete in a two-dimensional policy space, we are able to test the importance of a reference point for party's decision making.
