A new analysis of Pew Research Center pre-election surveys conducted this year finds that support for Republican candidates was significantly higher in samples based only on landlines than in dual frame samples that combined landline and cell phone interviews. The difference in the margin among likely voters this year is about twice as large as in 2008.
Data from Pew Research Center polling this year suggest that the landline-only bias is as large, and potentially even larger, than it was in 2008.
Fully a quarter of the U.S. adult population now relies solely on a cell phone. This paper shows that the potential for bias in telephone surveys that do not include cell only adults has grown since 2006. Of 72 questions examined on a wide range of topics - including political and social attitudes, personal and national economic ratings, foreign policy views, and attitudes toward and the adoption of a wide range of internet and communications technologies - cell phone samples made a difference of 3 percentage points or more on 29 of the questions. In 2006, on 46 questions examined none of the differences exceeded 2 percentage points.