Since 2002 (and probably earlier), you could do pretty well in predicting the outcomes of races for President, Senate, Governor and even the U.S. House by collecting the final polls in each race and averaging them. In fact, in 2008, the final Pollster.com trend estimates and RealClearPolitics averages did as well or better at calling election outcomes as those more "sophisticated" models you heard so much more about last year.
The reason is that while highly variable, the final polls were largely unbiased in the aggregate. Any one poll might be way off from the final result, but the average of all of them usually comes reasonably close to the final result. There have certainly been exceptions in individual states, but in 2002, 2004, 2006 and 2008, the polls looked reasonably accurate once averaged across all states.
We may perceive things differently tonight. First, instead of watching polling across 20 or 30 contests, most of us are focused on just three or four races and for two of these -- New York's 23rd District and the Maine Question 1 -- we have only one or two recent polls to consider.
Second, as Nate Silver pointed out yesterday, the challenges in some of today's elections -- again, especially Maine and NY-23 -- may be more like what pollsters faced during last year's presidential primaries, where poll averages often missed the mark by wide margins.
Silver also posted a handy comparison of final poll averages in New Jersey elections since 2000 (below), which helps make two important points. First, as he writes, despite conventional wisdom to the contrary there has not been "any particular tendency by Democrats to outperform their numbers once the final polls are in." Second, though usually very close to the result, final poll averages in individual states typically missed the final margin by a few percentage points. So even though our final New Jersey trend estimate is a remarkable 42.0% to 42.0% tie, for example, the final margin will be close but probably not that close.
Which brings me to our final polling-wrap up for 2009. Here's what the final polls and our trend estimates are showing:
- New Jersey, again, ends up as 42.0% to 42.0% tie on our trend estimate, a contest simply too close to call between Democratic incumbent Jon Corzine and Republican challenger Chris Christie, with independent Chris Daggett running far behind at 10.1% and likely falling. My hunch, explained last night, is that Christie prevails.
- New York's 23rd District special election for Congress was the focus of much speculation over the weekend. The last two polls, both conducted immediately after original nominee Dede Scozzafava withdrew from the race, each had Conservative Doug Hoffman leading Democrat Bill Owens, but by widely different margins (5 and 17 percentage points). Our trend estimate, which has Hoffman leading by 7 points (43% to 36%) also factors in previous polling that showed a closer contest. The ultimate margin is anyone's guess, but my sense is that Hoffman will win comfortably.
- The outcome of Virginia's race for Governor has never been in much doubt. Republican Bob McDonnell began with a roughly 7-point lead over Democrat Creigh Deeds that never significantly wavered, widening to nine points by Labor Day and ending at our final trend estimate of roughly 14 points (55% to 41%).
- Ditto for the New York City Mayor's Race. Incumbent Michael Bloomberg led Democratic challenger William Thompson consistently on polling throughout the race, although his lead on our final trend estimate (53% to 39%) is sightly narrower than earlier in the year.
- And the very few polls on Maine's Question 1, the gay marriage referendum, show a close contest, although as I wrote earlier this afternoon, referenda polling is notoriously error prone. The age composition of the PPP survey seems closer to plausible than the final DailyKos/Research 2000 survey, but beyond that, your guess is probably as good as mine.
Two notes on what's coming up later tonight. First, the consortium of network news organizations (known formally as the National Election Pool or NEP) is conducting exit polls in New Jersey and Virginia tonight. While official results will not begin to appear until the polls close, some early leaked estimates will probably start to bounce around the internet sometime after 6:00 p.m. As I explained at about this time last year (on on most election days since 2004), these are not likely to be much more accurate than the pre-election polls summarized above. Very large grains of salt are in order.
And finally, we will be live blogging here once again tonight. If all goes well, we should be using a more advanced tool that will allow our all-star line-up of contributors (Charles Franklin, Kristen Soltis, Margie Omero, Steve Lombardo and hopefully more) to join in. We hope you'll join us starting at about 6:30 eastern time.