Over the last few days, thousands of words have been written and many charts posted on Pollster and elsewhere, all trying to make sense of the sometimes divergent Massachusetts Senate polls. If you haven't yet, make sure you read Charles Franklin's tour de force review posted here a few hours ago, that walks through eighteen permutations of trend line models, all of which show Republican Scott Brown leading Martha Coakley, most showing him ahead by 4 points or more.
If you prefer a simpler summary, consider this:
- Of eight surveys completed and released since Wednesday, seven show Brown leading by at least a point. The one exception shows a dead heat Our chart of all polls shows a nearly seven point Brown gap between the trend lines for Brown and Coakley (51.2% to 44.3%).
- Browns' support on our standard trend estimate has increased by nearly twelve points (from 38.5% to 51.2%) in just the last two weeks.
A trend this strong is unusual, especially in a contest between a Democrat and a Republican. We do see such surges occasionally in primary elections -- the surprise victory by Creigh Deeds in last year's surprise victory in Virginia's Democratic primary being the most recent example -- but they are far more rare in general election contests . Over the weekend, I reviewed the most competitive contests we have tracked on Pollster.com since 2006 and found no race that produced a trend anywhere near this strong over the last few weeks of the campaign.
I am sure that there are other example, but the one that stands out for me is the victory of Democrat Harris Wofford in 1991. Wofford, appointed earlier that year to fill a vacant Senate seat, began as a virtual unknown and began trailing by more than 40 points against popular former Republican Governor Dick Thornburgh. Although the final round of public polls showed the candidates running about even, Wofford's momentum helped carry him to what turned out to be an eleven point victory margin (55 percent to 44 percent).
Of course, the same factors that make the trend toward Scott Brown so unusual also make the polling challenging and potentially misleading. Brown has moved up so rapidly partly because campaign has been truncated, but the rapid change also prompted a late avalanche of negative advertising by the Democrats directed at Brown. Because it is a special election being held on an usual date, Pollsters have no prior history to judge the size and demographics of the likely electorate. The likely voter problem is one reason why polling errors tend to be larger in special elections.
So while we have the Wofford experience on one hand, we have the lessons of the New Hampshire Democratic primary in 2008 and the special election in New York's 23rd District this past fall on the other. In both cases, candidates surged in the final polls, only to see their apparent leads disintegrate on Election Day. What those races had in common were huge surprise developments that occurred a few days days before the election (Barack Obama's Iowa victory and the withdrawal of Dede Scozzafava) that helped shake up the race, fuel the polling surge and -- perhaps -- provoke voters to focus more closely on their choices and rethink their preferences in the final hours.
Does the nationalization of the Massachusetts Senate race combined with the heavy negative advertising blitz qualify as the same sort of last minute surprise? Perhaps, but it seems like a stretch to me.
Some believe that non-response bias may have contributed to the errors in those two races, exaggerating the contribution of the most enthusiastic supporters of the surging candidate. Mike Mokrzycki developed that theory in the context of the Massachusetts Senate race here over the weekend. Some believe this phenomenon may be more acute in automated surveys, and we should not ignore that only two of the last seven public polls used live interviewers.
Yes, Coakley has done better on live interviewer surveys than the automated polls, but we saw a similar pattern in New Jersey last fall, and the robo-polls ultimately provided a closer forecast of the final margin.
Yes, the internal Coakley campaign poll numbers that have leaked out show a dead even race and perhaps a slight improvement over last week. However, there was more than one internal poll conducted by Democrats A little birdie tells me that the final tracking survey conducted by the Mellman Group for the Democratic Senatorial Campaign Committee had Brown ahead by five points.
So for me it boils down to this: I was a Democratic consultant for long enough to want to believe that Coakley can still prevail, and there is still a remote chance that the polls in this race will be as misleading as they were in New Hampshire. However, my head is not my heart. Barring another polling meltdown, Scott Brown is the likely winner.
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