response rates are confounded by survey sponsorship, with the federal government in the United States conducting or sponsoring most of the face-to-face data collection.

The one consistent finding with respect to the effect of mode of data collection suggests that to the degree the information is considered sensitive or socially undesirable, one is more likely to collect more accurate data via self-administrative modes of data collection. For example, although the National Household Survey of Drug Abuse is conducted as a face-to-face interview, questions concerning illicit drug use and other sensitive behaviors are reported via self-administration. The choice of multiple modes of data collection may be desirable from the perspective of reducing coverage bias (e.g., dual-frame sampling designs) or improving response; however such a design decision to reduce errors of nonobservation may come at the expense of an increase in measurement error.

Self and Proxy Response Status Should only self-response be accepted for household surveys of disability? If so, what are the ramifications on nonresponse bias? If proxy responses are accepted, what impact does this design choice have on the measurement error properties of the reporting of disability?

The use of proxy reporters—that is, asking individuals within a sampled household to provide information about other members of the household—is another design decision that is often framed as a trade-off among costs, sampling errors, and nonsampling errors. The use of proxy informants to collect information about all members of a household can increase the sample size (and hence reduce the sampling error) at a lower marginal data collection cost than increasing the number of households. The use of proxy respondents also facilitates the provision of information for those who would otherwise be lost to nonresponse because of an unwillingness or inability to participate in the survey interview. However, the cost associated with the use of proxy reporting may be an increase in the rate of errors of observation associated with poorer-quality reporting for others compared with the quality that would have been obtained under a rule of self-response.

The limited literature comparing self- and proxy reports in the measurement of disability has focused on the reporting of activities of daily living (Mathiowetz and Lair, 1994; Rodgers and Miller, 1997). Persons for whom data are obtained by proxy are often classified as having more functional limitations than those for whom the data are obtained by self-response; research is inconclusive as to whether this discrepancy is a function of overreporting on the part of proxy informants, underreporting on the part of self-respondents, or both.



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