Despite exhaustion and sleep deprivation, we want to take a few minutes today to a very quick and very preliminary look at how the preelection polls did as compared to yesterday's results. Since some precincts are still out and some absentee and provisional ballots are still being coutned, this quick looks is inherently preliminary and subject to change, but at the statewide level, the average of the last five polls in each races did reasonably well. In every case that we have examined so far, the leader in the average of the preelection polls was the leader on election day.
The following table includes only the most competitive Senate races that we tracked for the Slate Election Scorecard. It shows the curernt unofficial result in each state as compared to our final last-5-poll average. Since the preliminary results we gathered had been rounded to the nearest whole digit, we did the same with the final average. Again, every leader in the polls ran ahead yesterday.
[Note: For brevity's sake, the table above displays the results for Joe Lieberman in the Republican column, although Lieberman ran under the "Connecticut for Lieberman" party and has pledged to caucus with the Democrats in the Senate].
The list of the most competitive Gubernatorial races shows the same pattern. While the averagse did not predict the winners perfectly, the leader in the prelection polls was the leader on election day in every case.
[Update: The original version of the above table omitted the Minnesota Governor's race, which as several commenters noted, is the one state where the nominal leader in the averages was not the winner on election day. My apologies for the omission -- more details in a comment below.
Averaging results is obviously an imperfect solution to pre-election poll variation. The outcome in many races was off the "last-5-poll" average by as much or more than the Minnesota Governor's race: The Pennsylvania Senate race, the Maryland races for Senate and Governor, and the races for Governor in Alaska and Michigan all featured results differing from the final average that were as large as Minnesota].
We hope to have a far more comprehensive analysis in a few days looking at more races and using vote return data that is closer to complete. And these comparisons obviously make no effort to allocate undecided voters or use any of the more sophisticated measures of survey error. But for now, the bottom line is that the last-five-poll averages gave a pretty good impression of the likely outcomes of each of these competitive races.