An outpouring of support for Obama, or a statistical anomaly? Photo credit: Sage Ross
A Bloomberg poll released June 20 has President Barack Obama polling well ahead of his Republican challenger, Mitt Romney. Among likely voters polled, 53 percent stated they would vote for Obama in November, and only 40 percent stated they would vote for Romney. While most of the polls conducted thus far in June have had Obama edging Romney, this 13 point margin is unprecedented, since five other polls have placed Obama’s lead between one and four percentage points. Is Obama on his way to a major polling surge, or was the Bloomberg survey flawed?
Bloomberg Poll Methodology
The poll was conducted by Selzer and Company, on behalf of Bloomberg National News. A pool of 1002 respondents were contacted between June 15 and June 18, 734 of whom identified as likely voters. While some poll questions were presented to the entire sample, the “for whom would you vote” question was only presented to the smaller sample of likely voters. Respondents were contacted by live interviewers via landline and cell phone. Results were weighted for age and race to be consistent with recent census data. The margin of error for the smaller sample of likely voters was +/-3.6 points.
Was the Poll Flawed
Although some conservatives in the blogosphere are quick to assume the poll must have been biased, pollster J. Ann Selzer points out that the methodology and sample were similar to a Bloomberg poll conducted by Selzer and Company in March, which had the candidates tied. Both polls had demographics that closely mirrored U.S. Census data. The samples were, however, broken down to include only likely voters, so it is possible that the demographics shifted, as information about the sub-sample has not been released. Polling expert Mark Blumenthal concludes that the high margin for Obama should be questioned, unless other polls start showing a similar spread. He does not, however, suggest that the methodology was flawed. The most likely scenario, according to Blumenthal, is that the poll was a statistical outlier.
Click to Read Page Two – Polling Science: What is an Outlier?
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