http://www.huffingtonpost.com/2010/10/13/pew-research-cell-phone-p_n_761760.html Does it matter that many polls -- including the vast majority that we are currently watching at the state and congressional district level -- do not call Americans who use only a cell phone and thus lack landline telephone service? Yes it does. It creates a growing bias that appears to benefit Republican candidates. That's the message of a new analysis released this afternoon by the Pew Research Center.
Since 2006, a rapidly increasing percentage of American households lacks landline phone service. The most recent government estimates find that one in four American households is reachable by cell phone only. Pollsters have been reluctant to sample and call Americans on their cell phones, partly because it costs more and partly because federal law requires hand dialing any call placed to a cell phone, which makes such calls less efficient and puts cell phone polling off limits to automated survey methodologies.
For the last four years, the Pew Research Center has conducted public opinion surveys involving separate, parallel samples of both landline and mobile phones. Their design allows for a comparison between combined samples of landline and cell interviews and samples based only on landline calls.
Before the 2008 election, they found that calling only landline phones introduced a "small but real" bias in favor of John McCain, an average bias of 2.3 percentage points on the margin on nine national surveys conducted between June and October of that year.
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