Are the presidential polls skewed?

[nomoon]

I made a scatter plot of Obama's lead vs apparent Democratic skew for various polls on 10/21/12. There is a definite trend. I got most of the skew data from http://www.unskewedpolls.com/, and I didn’t verify that accuracy of all of the skew data. I checked some of them, but Rasmussen and Gallop were among those I couldn’t find party affiliation weighting.

The trend line isn’t a curve fit. I simply drew a line with a slope of one, which would represent the trend that would occur of all of the Obama advantage was proportional to the party weighting. The trend does suggest that much of the difference in polling results can be explained by different weighting schemes for predicting likely voters. It’s not a perfect fit, but it does appear to fit within the margin of error.

I saw an interview with a lead polling editor at Gallop. Gallop has published polling results that is more favorable for Romney, and has received criticism from the Obama campaign and other Obama advocates. Near the end of the interview, the interviewer asked him about apparent skewing among polls, but the Gallop editor didn’t seem to address the question directly. I’m paraphrasing, but he said that “we don’t do any weighting based on political party affiliation.” He seemed to imply that their weighting is determined by other metrics, and that there may be legitimate factors which may affect likely turn out, and that their results would reflect those changes in turnout.

However, the Gallop editor’s explanation still seems problematic to me. How could Romney be winning by 6 to 7 points, when Democratic turnout still gives Obama a one point advantage? From one I’ve seen, there isn’t much crossover voting from the political parties. Therefore, a huge proportion of the independents would have been polling for Romney. If Independents were favoring Romney so strongly, I would suspect that the Republicans would also be much more energized, and this would be reflected in a much highly likelihood (and thus, weighting) for them to vote than Democrats.

Some other thoughts:

• For some of the polls which appear to be heavily skewed for Obama (6 to 9 points), either the independents are enormously favoring Romney, or a significant fraction Democrats are crossing over for Romney. Regardless, such enthusiasm for Romney among independents and Democrats would be inconsistent with such a low relative turnout among Republicans. This is also contrary to polling results which state that Republicans are more energized than Democrats for their candidate.
• Rush Limbaugh has a theory that most of these Obama-leaning polls are intentionally skewed in order to push support for Obama. He also believes that these polling agencies will attempt to salvage credibility by unskewing their polls shortly before the election so that they can claim to have been accurate. It will be interesting to watch to see whether the amount of apparent skewing declines as we near the election.
• I’m still eager to hear an explanation for the possibility that the polls aren’t really skewed. If you have a alternate theories, I’d love to hear from you.
  

EDIT (10/23/12 8:45 PM CDT): I corrected the trendline to show the correct slope of 1.