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Study: Cell phones tilt polls

I’ve held a long-standing opinion that pollsters don’t contact people who use cell phones when conducting political polls, thus making the result less accurate. 

Now a report has come out confirming what many progressive bloggers have felt all along:  polls that had no input from cell phone users tend to favor Republicans…

Politico

This month’s election results lent support to what many pollsters have long suspected: Polls that don’t include cell phones favor Republicans.

And as more Americans come to rely on cell phones, the disparity is widening, according to a study released Monday by the Pew Research Center.

Pew’s surveys that included cell phones were dramatically closer to the actual midterm election results than they would have been without cell phones in the sample, according to the report.

A national Pew poll conducted days before the election found likely voters preferring a Republican to a Democrat for their representative in Congress by a 6-point margin when both land lines and cell phones were surveyed.

That margin closely matches the national vote for House candidates, according to the latest count: Republicans led by a 7-point margin.

But if the Pew pollsters had called only land lines, disregarding their cell phone sample, they would have found the GOP ahead by 12 points.

The new study bolsters the argument that polls that don’t call cell phones will be systematically biased. Calling cell phones poses numerous challenges for pollsters — from the difficulty of determining where respondents live based on their cell phone numbers to the fact that machine-aided dialing of cell phones is illegal.

While previous Pew reports had found a gulf between its overall sample and its land-line-only sample, the election result shows which one was right. The winner, clearly, was the sample that included both.

The election result “is a very good opportunity to evaluate the effectiveness of your methods,” Pew’s director of survey research, Scott Keeter, said. “We don’t have that many opportunities to have that kind of validation.”

And while Pew looked for evidence of a gap only in its own polling data, an independent analysis found a similar gulf existed at polling firms using different methods during the 2010 cycle.

The six national polling firms that surveyed both cell phones and land lines in the week before the election put Republicans ahead by an average of 6 points, while the four that called only land lines showed a GOP advantage