Telephone surveys have traditionally been conducted only by landline telephone. However, now that almost one-in-four Americans have a cell phone but no landline telephone service, more surveys are including interviews with people on their cell phones. For certain subgroups, such as young adults, Hispanics and African Americans, the cell only rate is even higher. Research has shown that as the number of adults who are cell only has grown, the potential for bias in landline surveys that do not include cell phone interviews is growing.

Growth in the Cell Only Population

Cell phone surveys are conducted in conjunction with a landline survey to improve coverage. The data are then combined for analysis. In addition to the issues associated with sampling cell phones, there are also unique challenges that arise when interviewing people on their cell phones.

One of the most important considerations when conducting cell phone surveys is that the costs are substantially higher than for a traditional landline survey. The cost of a completed cell phone interview is one-and-a-half to two times more than a completed landline interview. Although some of the fixed costs associated with landline surveys are not duplicated when a cell phone sample is added (such as programming the questionnaire), other costs are higher (data processing and weighting are more complex in dual-frame surveys).

Cell phone surveys are more expensive because of the additional effort needed to screen for eligible respondents. A significant number of people reached on a cell phone are under the age of 18 and thus are not eligible for most of our surveys of adults. Cell phone surveys also cost more because federal regulations require cell phone numbers to be dialed manually (whereas auto-dialers can be used to dial landline numbers before calls are transferred to interviewers). In addition, respondents (including those to Pew Research surveys) are often offered small cash reimbursements to help offset any costs they might incur for completing the survey on their cell phone. These payments, as well as the additional time necessary for interviewers to collect contact information in order to reimburse respondents, adds to the cost of conducting cell phone surveys.

Most cell phones also have caller identification or other screening devices that allow people to see the number that is calling before deciding to answer. People also differ considerably in how they use their cell phones (e.g., whether they are turned on all the time or used only during work hours or for emergencies). The respondents’ environment can also have a greater influence on cell phone surveys. Although people responding to landline surveys are generally at home, cell phone respondents can be virtually anywhere when receiving the call. Legal restrictions on the use of cell phones while driving, as well as concerns about safety, also have raised the issue of whether people should be responding to surveys on their cell phones while driving. In addition, people often talk on their cell phones in more open places where they may have less privacy; this may affect how they respond to survey questions, especially those that cover more sensitive topics. These concerns have led some surveyors (including the Pew Research Center) to ask cell phone respondents whether they are in a safe place and whether they can speak freely before continuing with the interview. Lastly, the quality of connection may influence whether an interview can be completed at that time, and interruptions may be more common on cell phones.

Response rates are typically lower for cell phone surveys than for landline surveys. In terms of data quality, some researchers have suggested that respondents may be more distracted during a cell phone interview, but our research has not found substantive differences in the quality of responses between landline and cell phone interviews. Interviewer ratings of respondent cooperation and levels of distraction have been similar in the cell and landline samples, with cell phone respondents sometimes demonstrating even slightly greater cooperation and less distraction than landline respondents.

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