For now, use the simple mean of all polls where the majority of interviews were conducted since August 1st, when the new political equilibrium began.
As the election draws closer, restrict the timeframe for polls included in the averages. During the final six weeks of an election, use the simple mean from the last 15 days.
Campaigns where one party is ahead by 6.0 or more are considered "solid." Campaigns between 2.7 and 5.9 are considered "leans." Campaigns within 2.6 or less are considered "toss-ups." These categories are subject to refinement based on continued research into past elections.
"Solid" and "lean" seats are considered pickups, while toss-ups are 50-50 for each party. States with mixed results will be considered 50-50 until the primary election. The overall forecast is the most likely seat change based on the current forecast. This is also subject to refinement.
Do not include Zogby Interactive polls and Columbus Dispatch polls, due to their horrendous past performance and questionable methodologies.
Do not include Strategic Vision polls, as it is starting to seem likely those are not real polls.
Include campaign-funded polls. Further, if there is more than one poll from a single organization, include all of them.
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.
Notes:
*= Faces primary, but heavy favorite
**= Not an announced candidate at this time
***= Faces serious primary challenges, but only candidate for which general election polling is available.
