The way PRRI assessed conservatism is derived from its American Values Atlas, a look at how people across the country feel about contested social issues: abortion, same-sex marriage and immigration. Using that data and comparing it to the rest of the country, the organization produced an index of cultural conservatism, from 1 (very liberal) to 7 (very conservative).
We've plotted values for the three early primary states PRRI considered and compared them to the national figures below. (The sample size of New Hampshire Republicans was too small to break out.)
In both South Carolina and Iowa, Republicans are more culturally conservative than Republicans nationally. But in Iowa, the right is much further right than the rest of the state.
If you look at how each state's vote for president has compared to the national vote margin since 2000, Iowa and New Hampshire are both slightly more Democratic than average. South Carolina is much more Republican. So the conservatism of Iowa's Republicans is even more notable, relative to the state's overall makeup.
On cultural issues, PRRI tells us, Iowa Republicans look a lot like South Carolina Republicans. Which helps explain why the state backed Mike Huckabee and Rick Santorum in back-to-back elections. (South Carolina, of course, backed eventual winner McCain in 2008, but broke a long string of winner-picking by supporting Newt Gingrich in 2012.) That outlier status might come at a cost: Neither Huckabee or Santorum came very close to the nomination.