For the measurement of political knowledge, researchers may prefer open-ended items to multiple-choice questions because they are concerned about blind guessing which leads to the overestimation of knowledge levels. In this research note, we distinguish informed guessing (i.e., guessing the correct answer based on partial knowledge) from blind guessing (i.e., guessing the correct answer randomly). We focus on college students and conduct a survey experiment with the techniques of confidence ratings. The results show that informed guessing is more common than blind guessing. We also show that, based on the results of our survey experiment, using multiple-choice items and the information on choice-options can appropriately reflect respondents’ knowledge levels.