Commentary: For the first time since I began monitoring the national House ballot since October, Democrats have fallen behind. Further, they have no clar path back into the lead, as five separate polling organizations now show them facing a deficit. This includes two of the three polling outfits with weekly poll updates, Daily Kos and Rasmussen.
It would be very difficult for Democrats to maintain control of the House of Representatives when facing a deficit like this. The median error for this methodology is 1.77%. As such, given current polling, the odds of a Democratic victory in the popular vote (if the election were held tomorrow) would only 32%. Given that Republicans have an edge in current district composition (the 218th district has a Cook PVI of R+2), that Republicans will likely have an edge in total number of districts with a candidate, and that many of these polls are still measuring all adults rather than registered voters or likely voters, if anything the Republican advantage of 1.2% is an underestimation.
Later in the month I will be introducing a House forecast that looks at individual seats. However, do not expect that more detailed, seat by seat forecast to be any more favorable to Democrats. Republicans are now in a position to retake the House. Barring any improvement in the national political environment, I expect them to do just that.
Do not include Strategic Vision polls, as it is starting to seem likely those are not real polls.
Include campaign-funded and partisan polls. Further, if there is more than one poll from a single organization, include all of them.
In the interests of a smoother average, polling outfits that release new generic ballot polls every week, such as Rasmussen, The Economist, and Daily Kos, will always have the same number of polls in the average (two).
The basic idea is to cram as many polls with sound methodologies into the averages as possible, and weight them evenly to include more overall data in the sample. Because voter preferences don't really change that much in high-profile elections, I thought this method might produce a more accurate result through logic of regression to the mean. It seems to work pretty well, as my research has shown so far.
This is different from my 2006 and 2008 methodology in that it includes polls from 15 days out from an election, instead of only 8. Further, campaign funded polls, and multiple polls from a single polling firm, are now included. All of these changes were made to include more polls in the averages, since my previous methodology was about 10-20% less accurate than Pollster.com and fivethrityeight.com. Since they had already raised the bar so high, and since they will probably improve their methodologies for 2010 even more, it was time for Open Left to step it up.
