Who will vote in the Iowa Republican caucuses? No one knows for sure: One thing polls have a hard time projecting is turnout. One indicator is past turnout, which Jennifer Rubin dissects in her Right Turn blog. The 2012 Iowa caucus turnout, according to the entrance poll, was 57 percent evangelical Protestant — the highest percentage for any Republican contest that year outside the South — and 83 percent had attended at least some college. Some 60 percent said they had voted in the previous caucuses in 2008.
This stands to reason. People aren't inclined to participate in something like an Iowa caucus unless they have done so before and/or if they are attending without at least one other friend. You don't want to spend an hour more in a room discussing controversial matters with dozens of people who are total or semi-strangers without having someone you know with you or without having done this before. This helps to account for the high evangelical percentages at Republican caucuses. Presumably they are part of congregation-based networks who attend as a group or with one or more friends. Unchurched people who don't participate in other civic associations are probably much more reluctant to go.
But is past performance an indication of future trend? Not always. Polls suggest that Donald Trump is attracting previous non-voters to his candidacy; the question is whether they will vote in primaries or — even iffier because of the above described circumstances — in the Iowa caucuses. And the answer is that we just don't know. We do know that about 125,000 Iowans voted in the 2008 and 2012 Republican caucuses. We know that about 250,000 Iowans voted in the 2008 Iowa Democratic caucuses, approximately double the number of Iowans who had done so in past years. We know that in statewide presidential year general elections about 700,000 Iowans vote for each party. Thus there are large reservoirs of additional caucus participants of both parties to draw on to increase caucus turnout.