What's Missing from National Landline RDD Surveys?
The Impact of the Growing Cell-Only Population
e-mail: skeeter{at}pewresearch.org
The number of cell phone only households has continued to grow – 12.8 percent of all households by the end of 2006, according to the National Health Interview Survey (NHIS). To assess the extent and nature of the potential bias in landline telephone samples created by the absence of cell-only households, the Pew Research Center conducted four independent dual frame studies in 2006, three of which included at least 200 interviews with cell-only respondents. Despite the fact that there are significant differences between cell-only and landline respondents on many important variables, across the four surveys with different substantive content we find that including a cell-only sample with a landline RDD sample produces general population estimates that are nearly identical to those from the landline sample alone. Yet, while the noncoverage problem is currently not damaging estimates for the entire population, we find evidence that it does create biased estimates on certain variables for young adults, 25 percent of whom are cell-only according to the most recent government estimate.
SCOTT KEETER is with Pew Research Center, 1615 L St., N.W., Suite 700, Washington, DC 20036, USA.
COURTNEY KENNEDY is with Pew Research Center and the University of Michigan, 426 Thompson Street, Room 4050, Ann Arbor, MI 48104, USA.
APRIL CLARK is with Pew Research Center, 1615 L St., N.W., Suite 700, Washington, DC 20036, USA.
TREVOR TOMPSON is with The Associated Press, 2021 K St., N.W., 6th floor, Washington, DC 20006, USA.
MIKE MOKRZYCKI is with The Associated Press, 168 Middle St., West Newbury, MA 01985, USA. The authors are grateful for the assistance of several individuals and organizations. Princeton Survey Research Associates International (PSRAI) and SRBI, Inc. collected the data reported here. The advice and assistance of Jonathan Best, Larry Hugick, Stacy Diangelo, and Julie Gasior at PSRAI, and Chintan Turakhia, Dean Williams, and Mark Schulman at SRBI was invaluable. Anna Fleeman, Charlotte Steeh, Linda Piekarski, Mike Brick, Clyde Tucker, and Stephen Blumberg regularly answered questions for us and provided us with updates from their own research with the cell phone population. The Pew Research Center and The Associated Press provided substantial support for the conduct of this research. We greatly benefited from the help and advice of Andrew Kohut, Michael Dimock, Nilanthi Samaranayake, Robert Suls, Greg Smith, Cary Funk, Juliana Horowitz, Richard Wike, Peyton Craighill, Lee Rainie, and John Horrigan. Paul Lavrakas and two anonymous reviewers provided excellent feedback on an earlier draft. The 2005 Cell Phone Sampling Summit II, organized by Paul Lavrakas and Chuck Shuttles, provided ideas and inspiration for this work.