In one of the most comprehensive investigations of fraud , Justin Levitt of Loyola Law School, Los Angeles turned up 31 credible instances of voter impersonation out of more than 1 billion votes cast between 2000 and 2014. Some of those cases may have been because of clerical errors. Levitt's investigation suggests that while voter impersonation does indeed happen, it happens so rarely that the rate is approximately one instance out of ever 32 million ballots cast. This is similar to the odds of getting “heads” 25 times in a row on a coin toss.