The UCal Berkeley Report

Exit Polls Legacy blog posts

First, one point I should have made more clearly in previous posts: The absence of significant evidence of fraud in exit polls does not prove the absence of fraud. When Warren Mitofsky says he sees no greater deviations for any particular type of voting equipment, he means he sees no differences big enough or widespread enough to be statistically meaningful. If vote fraud occurred in just a few counties in one state, the exit polls may have lacked the statistical power to detect it. That lack of power is what statisticians call “Type II Error.”

Which brings me to the U.Cal Berkeley report, (now available here – you need to scroll down to the link, “The Effect of Electronic Voting…).” The first thing to understand about the report, in the context of my recent posts, is that has nothing to say about exit polls. It depends in instead on a statistical analysis of county level voting patterns.

“Observer,” a commenter on my last post, made that point and also did a nice summary of the report’s findings:

They are using multivariate linear regressions to explain voting patterns in Florida, and are finding a very statistically significant correlation between the presence of electronic voting and a higher percentage for Bush.

The paper has undergone some peer review prior to publication. It mentions two concerns that were raised about the methodology, and shows that when those concerns were addressed the findings did not change substantially.

Of course, now that the paper has been released on Internet it will be subject to a much wider review by others with far more expertise in statistical modeling than I can offer. 

For now, just keep in mind that is possible that the Berkeley report detected a discrepancy that the Florida exit poll missed, given the size of the discrepancy and the number of precincts sampled.  It is also possible that the full report on the Florida exit poll will contradict the Berkeley finding.  Once again, without more specific data from NEP, we really cannot say for sure.

Corrected mispellings of Berkeley 11/19.

Mark Blumenthal

Mark Blumenthal is political pollster with deep and varied experience across survey research, campaigns, and media. The original "Mystery Pollster" and co-creator of Pollster.com, he explains complex concepts to a multitude of audiences and how data informs politics and decision-making. A researcher and consultant who crafts effective questions and identifies innovative solutions to deliver results. An award winning political journalist who brings insights and crafts compelling narratives from chaotic data.