I have been trying to determine whether President Obama’s current standing in the polls is running ahead or behind this time four years ago. To answer this question I’ve collected all the polling reports from RealClearPolitics for the 2008 election and all those for 2012 with fieldwork ending on or before October 7th. From here on I will refer to the day a poll’s fieldwork ends as its “polling date.” I then use this date to determine the number of days between the polling date and Election Day. I can then plot the President’s course in the polls in both years using an identical metric, the number of days remaining before Election Day.
I have chosen to focus on just those polls whose polling dates fell after July 4th. By then both parties have chosen their candidates, the campaigns have begun gearing up for the long haul to November. but no conventions or debates have taken place. I am also using only polls of “likely voters.” There are significant and complex differences in results between polls of likely and registered voters. To avoid all those confounding problems I am sticking to just likely voters.
That leaves us with 47 polls in 2012 and 119 polls from 2008 whose polling date fell after the Fourth of July and before Election Day. If we fit a straight line to all these polls using simply the time left before the election we get the graph above. The individual polls are represented by blue plus signs for 2008 and red Xs for 2012. (The red and blue colors have no partisan meaning; they are just designed to enhance visibility.) The horizontal axis is reversed so that it begins 125 days in advance of the election and ends on Election Day itself.
In general the graph depicts a fairly rosy view of the President’s chances. The one disturbing outlier is the Pew poll released today which had Mr. Romney ahead by four points among likely voters. The President faced a couple of equally bad polling results in 2008, but they occurred about a month earlier than Pew’s post-debate polling date of E-30. In 2008, the President consistently held the lead in every poll taken over the last thirty days of the campaign. At no time was he trailing in any poll this close to Election Day, never mind trailing by four points.
That caveat aside, 2012 has generally followed the same trajectory as 2008, though with the President running perhaps one percentage point behind his 2008 average. This estimate is still statistically weak reaching only the 0.10 level of significance, but I have included it since the number of 2012 polls is still fairly limited.
(There does not appear to be an “interaction” effect where the slope differs significantly in 2012 as well as the intercept. The best fit uses just a zero/one dummy for the 2012 election year along with the DaysBefore trend.)
The heavy line represents the best estimate for the trend taking all the elections together. The 2012 trend might run about one percent lower than 2008 as represented by the narrow line. If the campaign followed that trend, President Obama would win re-election by a margin of 53-47. Using the graph of the Electoral College “swing ratio” I posted the other day, that margin in the popular vote would translate into just under two-thirds of the Electoral Cellege, or over 350 Electoral Votes.