There are many rules of thumb in evaluating polls, especially in the volatile context of a primary. We usually caution people to look at polling averages rather than individual polls for a variety of reasons, not least the fact that some pollsters may have biases (even if unintentional) or may consistently produce outliers. Sometimes, of course, one pollster that sees the world differently from everyone else is right, so being way off the averages probably means the pollster is wrong, but it doesn't always.
So it is right now with American Research Group (ARG) in the New Hampshire Republican race. The RCP poll average right now has Ohio Governor John Kasich second in New Hampshire, far behind Donald Trump at 31 but with 13.3% to 11.5 for Marco Rubio, 11.3 for Ted Cruz, and 8.3 each for Chris Christie and Jeb Bush.
But the polling averages are heavily influenced by the lastest poll from ARG, which has Trump 27, Kasich 20, and Rubio 10 with everyone else in single digits. If we look at the Huffpost Pollster average, we can see what the averages look like with different pollsters in and out of the average:
The last three ARG polls had Kasich at 20, 14 and 15, while the majority of other polls the past several weeks had him in single digits. And since most of the other candidates do almost as well in ARG as elsewhere, what ARG is showing is Kasich drawing that extra support from...Donald Trump. And maybe that's right, given Trump's appeal to more liberal and moderate Republicans and independents, but it seems pretty implausible given their diametric styles - Kasich is the ultimate establishment Republican, a bleeding heart moderate who's been in office since the 1970s and likes to brag about running the House Budget Committee 20 years ago. ARG has a justifiably poor reputation as a pollster. FiveThirtyEight's pollster ratings, last updated before the 2014 elections, gave it a C+. Down the stretch run in 2012, it significantly overestimated Mitt Romney's performance in New Hampshire:
It also had Ovide Lamontagne up six in its last (early October) 2012 poll of the Governor's race, which he lost by 12 points - an 18 point miss.
Its final polls in 2014 had the Senate race tied (Shaheen won by 3) and Maggie Hassan up by 2 after leading by 15 and 10 in the two prior ARG polls (Hassan won by 5).
So, this may be the time when ARG is right, but the smart money wouldn't bet on it.