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New Hampshire presidential primaries are hard for pollsters to get right. In the Granite State, independents can pick which primary to vote in and citizens can register same-day.

Most polls, for instance, didn’t pick up Hillary Clinton’s late surge in 2008. Technically, this year was easier given that there wasn’t a race on the Democratic side. There was also little polling drama surrounding the frontrunner before Tuesday's vote.

Mitt Romney’s numbers had consistently hovered between the mid-30s and low-40s, and none of his rivals were above 20 percent. But Ron Paul ended up with 23 percent of the vote when all was said and done in New Hampshire. 

When we look at the polls that were conducted after the Iowa caucuses, Romney was at a high of 42 (NBC/Marist poll) and a low of 35 (Suffolk and PPP Polls). Romney’s average number over the last week was 39 percent and the final three polls in the race (American Research Group, Suffolk and Rasmussen) had him at 37 percent. The former Massachusetts governor, according to the polling, had this one locked in. His final number of 40 percent was right on the mark.

Rick Santorum and Jon Huntsman had both gained steam over the past week, although Huntsman has a much higher support ceiling than Santorum. Since Iowa, Santorum had been consistently in the low teens, with most polls putting him at 11 percent. Huntsman has been showing a clear surge over the past week, going from 7-8 percent in most polls to 15-18 percent in the last few days. ARG had Huntsman in second place in their last poll out the morning of the primary.

Paul is typically a very consistent candidate when it comes to polling and results. His supporters are loyal, but aren’t typically welcoming newcomers. Polling had him between 17-18 percent going into primary day. Paul, however, did better than the polling suggested, finishing with 23 percent of the vote.

As for the rest, the polling caught the Huntsman surge and were quite accurate on hitting his numbers. The polling was also mostly on the mark for Gingrich, Santorum and Rick Perry.

The miss on the Paul numbers is a bit troubling. When looking at the polling firms that release their demographics, it is clear that younger voters were under sampled. In the last Suffolk Poll, under 35s were at 7.6 percent; PPP had under 30s at 10 percent. Moreover, both these firms were also off on the sampling of independent voters. PPP had independents at 37 percent and Suffolk had them at 40 percent.

According to exit polls, independents made up 47 percent of the electorate. I hate to pick on the firms that actually release their data since this should be encouraged, but these under samplings seems to have shown Paul lower than he should have been and therefore Huntsman showing to be in a better relative position. Given the relative uniformity in the polling one can safely assume the other firms had similar issues.

Given Romney's wide lead in New Hampshire, the under sampling of independents and younger voters didn’t throw the polls off wildly. But in South Carolina, where the candidates are packed much tighter, a similar missampling could be much more consequential.

Stefan Hankin is founder and president of Lincoln Park Strategies, a Washington D.C.-based public opinion firm. Follow him on Twitter at @LPStrategies