National House Ballot Update, November 8th

by: Chris Bowers

Sun Nov 08, 2009 at 17:59

Nov 08: Democrats +5.63

Last update: Nov 07: Democrats +5.18

Polls included in the calculation

Poll Sponsor Poll Mid-Date Democrats Republicans

Total Nov 08 42.75 37.13

Daily Kos Nov 04 35 30

Economist Nov 02 46 37

AP Oct 31 48 41

CNN Oct 31 50 44

Rasmussen Oct 29 38 42

Daily Kos Oct 28 36 28

Economist Oct 26 47 41

NBC / WSJ Oct 24 46 38

Rasmussen Oct 22 38 42

Daily Kos Oct 21 37 28

Economist Oct 19 45 36

PPP Oct 18 48 40

ABC / WaPo Oct 17 51 39

Rasmussen Oct 15 37 42

Daily Kos Oct 14 35 29

Economist Oct 12 47 37

Chris Bowers :: National House Ballot Update, November 8th

Methodology:

Until the final six weeks of the election, take the simple mean of virtually all polls where the majority of interviews were conducted over the last 30 days.
During the final six weeks of an election, use the simple mean from the last 15 days.
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.