Reality check 101: The need for unbiased polling

When Internal Polls Mislead, a Whole Campaign May Be to Blame

By NATE SILVER, NYT

Pollsters can expect to take their share of blame when their campaigns lose, and this year has been no exception. Not long after Barack Obama and Democrats had a strong night on Nov. 6, Republicans began to complain publicly that the polls conducted by their campaigns and by affiliated groups implied considerably more optimistic outcomes for them than actually occurred.

Perhaps these Republicans shouldn't have been so surprised. When public polls conducted by independent organizations clash with the internal polls released by campaigns, the public polls usually prove more reliable.

Take, for example, the gubernatorial recall election in Wisconsin earlier this year. Independent polls had the Republican incumbent, Scott Walker, favored to retain his office by about six percentage points. A series of polls conducted for Democratic groups showed a roughly tied race instead.

Mr. Walker in fact won by seven points: the independent polls called the outcome almost exactly, while the internal polls were far from the mark.

(More here.)