Voter preferences do not remain static. It is not hard to find cases where the outcome of an election remained uncertain until the last minute because of swing voters. The panel survey has the benefit of being able to track changes in the perceptions and attitudes of voters on major political and social issues in Korea by carrying out multiple surveys with groups of respondents that are representative of the larger voting population. EAI has carried out panel surveys during major elections, and voter preferences during the early elections held in 2017 following the impeachment of the former president were found to be particularly unpredictable up until the last minute. We also analyzed the factors that influenced those preferences, revealing the degree to which elements such as the candidate themselves as an individual, party preference, the political issues of the THAAD installation and presidential impeachment, and media influence, particularly televised debates, made an impact. EAI hosted a seminar in conjunction with the Legislative Research Agency titled "The 2017 Presidential Election and the Future of Korean Democracy" where the major results of this research were announced. In consideration of the academic value of these panel surveys for future electoral research, the series The Changing Preferences of Korean Voters was subsequently published.