In research and data science, we sometimes encounter biased data: that is, data that has not been sampled completely randomly and suffers from an over- or under-indexing toward the population of interest. Survey data is an example in this regard. Surveys play an important role in providing measurements on subjective user experience indicators, such as sentiment and opinions, which cannot be measured by other means. But because survey data is collected from a self-selected group of participants, it needs to be analyzed carefully.