Theoretically the process of contacting a sample household, once located, is rather straightforward. As Figure 1-4 shows, the success at contacting a household should be a simple function of the times at which at least one member of the household is at home, the times at which interviewers call, and any impediments the interviewers encounter in gaining access to the housing unit. In face-to-face surveys the latter can include locked apartment buildings, gated housing complexes, no-trespassing enforcement, as well as intercoms or any devices that limit contact with the household. In telephone surveys, the impediments include caller ID, call blocking, or answering machines that filter or restrict direct contact with the household.
FIGURE 1-4. Influences on the likelihood of contact with a sample household.
SOURCE: Groves and Couper (1998)
In most surveys the interviewer has no prior knowledge about the at-home behavior of a given sample household. In face-to-face surveys interviewers report that they often make an initial visit to a sample segment (i.e., a cluster of neighboring housing units sampled in the survey) during the day in order to gain initial intelligence about likely at-home behaviors. During this visit the interviewer looks for bicycles left outside (as evidence of children), signs of difficulty of accessing the unit (e.g., locked apartment buildings), small apartments in multi- unit structures (likely to be single-person units), absence of automobiles, or other signs. Sometimes when neighbors of the sample household are available, interviewers seek their advice on a good time to call on the sample unit. This process is the practical method of gaining proxy information about what call times might successfully encounter the household members at home. In telephone surveys, no such intelligence gathering is possible. The only information about at-home practices of a sample household is obtained by calling the number. (This imbalance leads to the larger number of calls required to make first contact with a household in telephone surveys; see Groves and Kahn, 1979.)
Information from time-use surveys, which ask persons to report on their activities hour by hour, has shown common patterns of at-home behavior by weekday mornings and afternoons, weekday evenings, and weekends. Those in the employed labor force are commonly out of the house, with the lowest rates of occupancy between 10 a.m. and 4:30 p.m. (Hill, 1978). Interviewers make repeated calls on households they do not contact on the first call. Their choice of time for those callbacks can be viewed as repeated samples from a day-of-week, time-of-day frame. They base their timing of successive calls on information they obtain on prior unsuccessful visits and on some sense of consistency. For example, interviewers often are trained to make a callback on a unit not contacted at the last visit on Tuesday afternoon, by visiting during an evening or weekend.
Physical impediments are sometimes so strong that they literally prevent all contact with a sample unit. For example, some higher priced multiunit structures have doormen that are ordered to prevent entrance of all persons not previously screened by a resident. Such buildings may be fully nonrespondent to face-to- face surveys. Similarly, although there is evidence that the majority of owners of telephone answering machines use them to monitor calls to their unit when they are absent, some apparently use them to screen out calls when they are at home (see Tuckel and Feinberg, 1991; Tuckel and ONeill, 1995), thus preventing telephone survey interviewers from contacting the household.
Other impediments to contacting households may offer merely temporary barriers, forcing the interviewer to make more than the usual number of calls before first contacting the households. For example, apartment buildings whose entrance is controlled by a resident manager may require negotiations with the manager before access to sample households is given.
Is there empirical evidence regarding the model in Figure 1-4? First, lets look at the distribution of the number of calls required to make first contact with a sample household. Figure 1-5 shows the proportion of sample households contacted by calls to first contacts. This figure displays the result for several surveys at once, some telephone and some face to face. The pattern is relatively stable across the surveys, with the modal category being the first call immediate contact with someone in the household. The proportion contacted on later calls is uniformly decreasing in subsequent calls. Rather uniformly, if the first call attempt is unsuccessful, the likelihood of contact declines with each successive call.
FIGURE 1-5. Percentage of eligible households contacted by calls to first contact.
Does the character of sample households vary by calls to first contact? Figure 1-6 shows an increasing percentage of the households are single-person households as the number of calls to first contact increases. Single-person households tend to be more difficult to contact. Other analysis shows that the exception to this tendency is single-person households with elderly persons, which tend to be home more often than other households.
FIGURE 1-6. Percentage of contacted households with one person, by calls to first contact (National Survey of Health and Stress).
Figure 1-7 shows a similar result for an access impediment in telephone surveys, the answering machine, which now is present in more than 50 percent of homes nationwide (Tuckel and ONeil, 1995). The percentage of contacted households with answering machines increases with each succeeding category of number of calls to first contact. Households with answering machines slow down contact with household members, requiring more calls to first contact.
FIGURE 1-7. Percentage of contacted households with ananswering machine by calls to first contact.
Other empirical results are similar to these could be presented. Households with access impediments slow down contact of interviewers with sample units. More calls are required to even deliver the survey request. Furthermore, households that are home less often require more calls; these include households where all adult members work out of the home during the day, urban versus rural households, and in telephone surveys, unlisted households.
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