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Man vs. Machine in New Jersey

There’s a rather strange split in the polls in New Jersey’s gubernatorial race: those conducted by live interviewers have Jon Corzine leading by an average of 4.2 points, but those conducted via IVR (automated scripts or “robopolls”) have Chris Christie leading by an average of 3.0 points. The difference is statistically significant with probability t=3.26, i.e. about a 98 percent chance that it isn’t the result of chance alone.

This is probably not a phenomenon local to New Jersey; PPP and Rasmussen have generally shown pessimistic numbers for Democratic numbers in other states thus far this cycle. An automated poll tends to be associated with lower response rates, since an automated script can’t do as much a human to coax someone into an interview, and therefore sometimes tends to reach a more enthusiastic set of respondents (in effect, it may serve some of the same functions as a very tight likely voter screen).

Since Republicans tend to be more enthusiastic right now, that may be what’s causing the automated polls to be more favorable to them. But since none of us yet know how the enthusiasm gap is going to play out in practice, it would be premature to come to any conclusion about whether the voter universe that Rasmussen and PPP are coming up with is “too tight” or “just right”. For that matter, I’m not yet ready to make a forecast for New Jersey; I certainly don’t see it as self-evident that Jon Corzine ought to be as much as a 2:1 favorite, which is where Intrade has him now.

Nate Silver is the founder and editor in chief of FiveThirtyEight.