With fully a quarter of the U.S. adult population now relying solely on cell phone service, pollsters and other survey researchers face a difficult decision as to whether to include cell phones in their samples.  A joint study by the Pew Research Center for the People & the Press and the Pew Internet & American Life Project takes an up-to-date look at the potential biases in findings based on landline-only surveys. Read the full report at PewResearch.org »