Lynn Vavreck reveals who they are:
While you’re more likely to be a ticket-splitter if you are a moderate or independent, the single best predictor of cross-party voting is still how much you know about politics: the less you know, the more you vote for two parties. … Despite a lot of evidence to the contrary, it is tempting to think that something as important as control of the Senate lies in the hands of voters who carefully pick and choose which candidates to vote for in each race on the ballot, but this seems unlikely. It is more likely that split-ticket voters are buffeted by idiosyncratic factors, like incumbency status, recent campaign advertising, and the tone and share of news coverage candidates receive.
The Dish 