Statistical Analysis of Polling Data

[xocolatl]

This analysis started as a discussion in another thread,
Want proof that FOX, CNN and AP rig the Polls? Here it is.

Thanks to TruthIsAll for providing the raw data.

Preliminary analysis in this post and this post suggest that FOX and AP are biased (either willfully or through selection bias) against Kerry, but CNN is equivocal.

The following table, generated from the same kind of crossed-effects model, shows the relative bias of each polling organization, ordered from least favorable to Kerry to most favorable (margin of error in parenthesis):


FOX: -3.5894 (1.5)
AP: -3.4184 (1.6)
NBC: -1.8152 (1.6)
CNN: -0.7108 (1.5)
IBD: -0.6136 (1.5)
TIME: -0.2378 (1.7)
PEW: -0.1133 (1.5)
ZOGBY: 0.4918 (1.6)
NWK: 1.1434 (1.5)
LA: 1.8013 (2.0)
CBS: 2.0928 (1.5)
ARG: 2.4043 (1.5)
ABC: 2.5649 (1.6)


Also interesting are the adjusted monthly spreads, showing a clear trend towards increasing support for Kerry, with possibly a slight dip in April and June (the numbers show point spread between Kerry and Bush):


Jan: -9.714 (2.1)
Feb: 0.7849 (2.1)
Mar: 2.3458 (2.1)
Apr: 0.6824 (2.1)
May: 1.8477 (2.0)
June: 0.4495 (2.1)
July: 3.6037 (2.1)


This analysis has some flaws, but they can't be corrected without knowing the sample size for each individual monthly poll.

[Renew Deal]

1. It's time to change your avatar

Thanks for the analysis

[troublemaker]

2. Are all ten likely voters or registered voters? (or mixed?)