With all the poll watching that goes on in elections these days, the question of how accurate the polls are has become more interesting (to me at least). I’ve been informally tracking the question of whether certain polling outfits tend toward liberal or conservative bias for quite some time. To be clear I’m not accusing any particular polling operation of purposeful bias, but rather just calling into question whether their methods (particularly of sampling, weighting, collecting data, and especially constructing likely-voter models) trend one way or another. In the case of the battleground areas, at least, that the pollsters–as a group–missed the mark is not a huge surprise, but the consistency in the pattern of that miss is more of a problem and suggests that they need a collective adjustment in how they are going about this.
To look at this, I took the 12 states still considered “toss-ups” by Real Clear Politics at election time (OH, FL, VA, NH, NC, MI, WI, PA, IA, CO, NV, MN) and calculated the difference between the “RCP Average” (of recent polls) and the percentage of actual vote in those states as of this morning. The result was that the RCP Average was conservatively biased (over-estimating support for Romney) in 11 out of the 12 states (Ohio being the only exception). The average miss was 2.4 points, which is probably within the “margin of error” of most of these polls, but the consistency of the direction of the error suggests that some re-tooling is necessary.