Pew: Cellular Polling Bias Hurts Obama
Here’s another reason to doubt the blizzard of polls that dominate political talk.
Pew, the respected non-partisan research organization, reports that polls that exclude cell phones may be a bit off — and effectively biased against Sen. Barack Obama. (H/T Michael Connery, and Mark Blumenthal has a good summary here.) Based on three recent election surveys:
[T]here were only small, and not statistically significant, differences between presidential horserace estimates based on the combined interviews and estimates based on the landline surveys only. Yet a virtually identical pattern is seen across all three surveys: In each case, including cell phone interviews resulted in slightly more support for Obama and slightly less for McCain, a consistent difference of two-to-three points in the margin… As implied by these results, in each of the three polls, the cell-only respondents were significantly more supportive of Obama (by 10-to-15 percentage points) than respondents in the landline sample.
Regular landline polling is supposed to account for these trends, but Pew concludes that’s getting harder:
[A] substantial minority of the cell-only sample is younger than 30 – a demographic group that has consistently backed Obama this year. Traditional landline surveys are typically weighted to compensate for age and other demographic differences, but the process depends on the assumption that the people reached over landlines are similar politically to their cell-only counterparts. **These surveys suggest that this assumption is increasingly questionable, particularly among younger people. **(emphasis added).
This finding — even with its caveats — complicates most current polling coverage, which barely discusses the margin of error, let alone inaccuracies in the age and cell sampling.
Republicans have been complaining about a press bias against McCain, maybe Democrats will start flagging the polling bias against their candidate — and his young, cell-toting supporters.
Photo Credit: Mike Kline Flickr