Michael Barone on Polling issues for this election

In today's WSJ:

It's not clear that race was the issue. Recently pollster Lance Tarrance and political consultant Sal Russo, who worked for Bradley's opponent George Deukmejian, have written (Mr. Tarrance in RealClearPolitics.com, and Mr. Russo on this page) that their polls got the election right and that public pollsters failed to take into account a successful Republican absentee voter drive. Blair Levin, a Democrat who worked for Bradley, has argued in the same vein in the New York Times. In Virginia, Douglas Wilder was running around 50% in the polls and his Republican opponent Marshall Coleman was well behind; yet Mr. Wilder won with 50.1% of the vote. . . .

And what about Barack Obama? In most of the presidential primaries, Sen. Obama received about the same percentage of the votes as he had in the most recent polls. The one notable exception was in New Hampshire, where Hillary Clinton's tearful moment seems to have changed many votes in the last days.

Yet there was a curious anomaly: In most primaries Mr. Obama tended to receive higher percentages in exit polls than he did from the voters. What accounts for this discrepancy?

While there is no definitive answer, it's worth noting that only about half of Americans approached to take the exit poll agree to do so (compared to 90% in Mexico and Russia). Thus it seems likely that Obama voters -- more enthusiastic about their candidate than Clinton voters by most measures (like strength of support in poll questions) -- were more willing to fill out the exit poll forms and drop them in the box. . . .