16% is ridiculously low. In 2012, 51% of Iowa GOP “likely caucusgoers” were Evangelical or “born-again” Christians: http://politicalticker.blogs.cnn.com/2012/01/03/iowa-caucus-goers-by-the-numbers/ (I don’t know whether this percentage was confirmed by the “entrance polls” that they carried out.)
To hear the media describe it in 2012, you'd think the demographics of Iowa citizens were about 99% "Evangelical" and 1% everyone else, since the ONLY religious group they ever discussed the voting habits of in Iowa was that group, and made it sound like they represent the beliefs of all Iowa voters.
I looked up the ACTUAL breakdown by religion in Iowa, and in reality its almost evenly split between white evangelical protestants (25%) and Catholics (23%). http://www.beliefnet.com/Faiths/2004/11/State-By-State-Percentage-Of-White-Evangelicals-Catholics-And-Black-Protestants.aspx# ) Protestants as a whole form a narrow 52% majority (so that means about 25% of Iowa voters are mainline protestant), making the state pretty balanced equally between different religious faiths and Christian traditions.
It's no Alabama-style bible belt state where everyone is born again, despite the media's attempts to portray it as such. It would be like claiming Australia (currently equally split three ways between Catholics, Anglicans, other Christian denominations) and is a gung-ho Roman Catholic nation and votes for whoever the Pope wants.
If Evangelicals make up a majority of Iowa caucus voters, then they must have a far greater turnout than any other religious faith in Iowa.