Exploring Unpopular Presidential Elections
  There have been several instances in our nation's history in which the presidential candidate who received the most popular votes did not win the presidency. Using a principal components analysis of recent presidential elections, we estimate the likelihood of such an outcome under modern conditions to be approximately 5%. We also investigate the effect on this estimate of eliminating from the Electoral College the two electors per state awarded due to their representation in the Senate, as well as the effect of increasing them. We conclude with an analysis of the likely consequences of The National Popular Vote Bill, which would award the presidency to the candidate with the largest national popular vote total if it took effect. 
Michael Neubauer, Mark Schilling, Joel Zeitlin
stat.AP