Guest Pollster | August 27, 2008
Today's guest pollster contribution comes from Michael P. McDonald, an Associate Professor of Government and Politics in the Department of Public and International Affairs at George Mason University and a Non-Resident Senior Fellow at the Brookings Institution.
A media storyline surrounding the Democratic convention is how a sizable number of Hillary Clinton supporters are backing John McCain over Barack Obama. A recent CNN/ORC poll provides grist for the mill. Twenty-seven percent of self-identified Clinton supporters are reported backing John McCain, an increase from 16% in a similar June survey.
Yet, there are indications that something is amiss in this survey. CNN reports they interviewed 1,023 adults. The organization does not report the sub-sample size of Democrats who support Clinton, but they do provide a margin of error of this sub-sample from which we can infer the number of Clinton supporters. The reported margin of error for Democrats who support Clinton is 7.5 percentage points, which is equivalent to 171 persons assuming a simple random sample. That is 16.7% of all adults in the survey, which when applied to my 2006 voting-age population estimate of 227 million persons means that there are 38 million self-identified Clinton supporters among Democrats in the CNN/ORC poll (with a 95% confidence interval between 20.9 and 54.9 million persons).
As one might recall, Clinton received 18 million votes in the primaries. If she had received 38 million votes, she would be accepting the Democratic Party's nomination on Thursday.
The question arises, who are these 20 million or so self-identified Democrats who support Clinton who did not participate in the primaries? It is difficult to tell without analyzing the survey in depth. While there are many reasonable explanations for the discrepancy between the election and survey results, a plausible explanation consistent with the large percentage of self-identified Clinton supporters who report supporting McCain in a two-way contest against Obama is that the CNN/ORC questionnaire is worded in such a manner that elicits persons who self-report supporting McCain to report that they are a Democrat who supports Clinton for the party's nomination.
The implication is obvious: if these surveys that purport to measure Clinton supporters who will vote for McCain actually measure McCain supporters who would like to see Clinton as the Democratic nominee, the media storyline of Democratic dissention quickly unravels.