Weighting marks an area where IBD/TIPP’s poll is more unusual on two fronts. First, the poll weighs its sample of registered voters to match 2014 Current Population Survey estimates for that group by age, gender, racial and region. By contrast, the most regular national surveys weigh their overall adult samples to demographics of the voting-age population, for which benchmarks are published with greater regularity. Although the IBD poll weights to different census population parameters than other surveys, it is not clear that this would necessarily boost Trump’s support in a survey without testing.
Education also was not a weighting factor in IBD’s survey, though it is commonly used in surveys since adults with less education tend to be hard to reach in public opinion polls. This year, lower- and higher-educated white voters have diverged sharply in their support for Clinton and Trump.
A second unusual aspect of IBD/TIPP’s weighting is party identification, where the survey’s sample of registered voters is weighted to match a predetermined estimate for the share of self-identified Democrats, Republicans, independents and others. Mayur declined to provide details on the source of party identification benchmarks, describing them as proprietary, although weighting sources are a required element of disclosure for the American Association for Public Opinion Research.
The IBD survey did not publish the partisan breakdown of registered voters but did release unweighted and weighted counts of likely voters. The survey’s unweighted sample found Democrats and Republicans tied on party identification (32 percent apiece), while weighted likely voters showed Democrats with a seven-point edge in party identification (35 percent to 29 percent). That margin is about similar to the average of party identification in recent live-interviewer phone surveys of likely voters by the Huffington Post, 36 percent Democratic and 31 percent Republican.
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