Pew Research Scott Keeter and Ruth Igielnik  In recent years, polling has missed the mark in several high-profile elections, drawing particular attention to the difficulties inherent in using surveys to predict election outcomes. These failures typically result from one or more of three causes: biased samples that include an incorrect proportion of each candidate’s supporters; change in voter preferences between the time of the poll and the election; or incorrect forecasts about who will vote. While not a new concern, the third of these – the difficulty of identifying likely voters – may be the most serious, and that is the focus of this study. Election polls face a unique problem in survey research: They are asked to produce a model of a population that does not yet exist at the time the poll is conducted, the future electorate.…Read more