and use it with some regularity, leaving a possible one-third of households unable to respond to a survey over the Internet from home.

Another problem that arises with creating a sample of Internet respondents is that it is harder to implement a within-household random selection because some householders lack Internet skills. In the case of some households, this phenomenon may be related to a division of labor: just as some people do the laundry and some take care of cars, a particular person in a household may use the Internet. Furthermore, survey organizations generally do not have email addresses that would enable them to send respondents links to Internet surveys, unless a prior relationship exists. Even if this could be resolved, it is likely that response to an initial email invitation would be quite low.

Meanwhile, the telephone is losing its viability as a survey mode option. There are many reasons for this, including the increasing use of cell phones (although these can sometimes be added to a frame), the decreasing reliance on landlines (current coverage is less than 75 percent of households), and increasingly blurred lines when it comes to the geography of phone numbers. American culture has also changed. People no longer use the telephone for most business interactions unless they have to, and they tend to exercise more control over their devices than in the past, by not always answering calls.

The telephone itself now fulfills a variety of functions, often serving as a personal computer. However, the screen space available for a web questionnaire is small, and entering text on a telephone is prone to error. Finally, responding to a survey on a phone device often cannot be combined well with other activities the potential respondent may be doing while accessing the Internet.

Changes related to the telephone and the continuing limitations of Internet access suggest that, in the near future, there will be more reliance on mixed-mode survey designs to collect data. Dillman devised a typology of the ways data collection modes are most commonly mixed (Dillman et al., 2009), summarized in Box 4-1.

The first type involves the use of a particular mode to encourage people to respond by another mode (typically, the Internet). In a sense, this is still a single-mode study, and therefore measurement differences between modes are not as big a concern as they might be otherwise. In the second type, one mode is used to ask some of the questions, and another mode to ask others, such as more sensitive questions. In practice, this interview technique often entails an interviewer simply turning a laptop around during a face-to-face interview so that the respondent can self-administer part of the interview. A third type of mixed-mode design involves using different modes of administration for different types of respondents. A fourth approach, typically used in longitudinal studies, employs one interview mode for the first interview and another mode for the second and subsequent interviews.

Dillman pointed out that it is important to remember when combining different modes of administration that sometimes achieving one survey objective

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