A comparison of responses to mailed questionnaires and telephone interviews in a mixed mode health survey.

This paper compares respondents to mailed questionnaires with those nonrespondents subsequently interviewed by telephone in a survey of Massachusetts women aged 45-55 years conducted in 1981-1982. This mixed mode approach produced 8,050 responses, giving a response rate of 77%. This rate is similar to rates obtained in many surveys that employed in-person interviews, which are still widely used in health surveys but are increasingly expensive. Telephone respondents differed socioeconomically from mail respondents, suggesting that telephone follow-up of nonrespondents may have reduced nonresponse bias in this survey. Thus, a mixed mode approach may be superior to a mail-only approach with respect to this aspect of data quality. Women responding by mail were more likely to hold professional jobs, to have relatively high household incomes, and to have more years of education. Controlling for these socioeconomic differences did not, however, remove differences in reported health outcomes between mail and telephone respondents. These differences may be explained by less complete recall in the telephone interviews or they may arise from actual differences in health profiles between early (i.e., mail) and late (i.e., telephone) respondents. Although a mixed mode approach may reduce nonresponse bias, more research is required concerning the reasons for response differences between modes and to eliminate any differences caused by problems in data quality.