About those Mason-Dixon polls that the Denver Post uses...

I picked up a Sunday Post this morning to read over breakfast and noticed that the battle-ground state polls they cited on their front page seemed to be more favorable to McCain than I expected. The poll the Post cited actually showed Obama up by only 4 in Colorado and McCain with a slight lead in Ohio. Needless to say that was news to me and I follow the polls very closely. The Post relies on Mason Dixon and today Nate Silver of FiveThirtyEight notes that,

The new set of battleground state polling from Mason-Dixon provides a terrific working example of what we call "house effects" -- a poll's consistent tendency to lean toward one candidate or another. Throughout this election cycle, we have found that Mason-Dixon's polls lean 2-3 points more toward John McCain than the average of other polls taken in those states at the same time...

to make this clear for the nth time, the presence of a house effect does not mean that a pollster is partisan or "biased". Mason-Dixon is a non-partisan pollster. Nor does it mean that a pollster is wrong! Mason-Dixon has a pretty good track record. Their vision of the electorate -- which seems to point toward a narrow Obama electoral victory -- could very easily turn out to be the right one. But it does mean that you need to take these sorts of things into account to make sure that you're making what you think are apples-to-apples comparisons.

In short, the Mason-Dixon polls have showed Obama underperforming his national average for some time now. The Mason-Dixon polls have, like most other polls, been relatively stable. There is no McCain surge evident in the polls. Good thing to keep in mind if you get calls from hyper-ventilating liberal friends worried about shrinking poll numbers.