The Factor Structure of the SF-36 Health Survey in 10 Countries

Many health status surveys have been designed for mail, telephone, or in-person administration. However, with rare exception, investigators have not studied the effect the survey mode of administration has on the way respondents assess their health and other important parameters (such as response rates, nonresponse bias, and data quality), which can affect the generalizability of results. Using a national sampling frame of noninstitutionalized adults from the General Social Survey, we randomly assigned adults to a mail survey (80%) or a computer-assisted telephone survey (20%). The surveys were designed to provide national norms for the SF-36 Health Survey. Total data collection costs per case for the telephone survey ($47.86) were 77% higher than that for the mail survey ($27.07). A significantly higher response rate was achieved among respondents randomly assigned to the mail (79.2%) than telephone survey (68.9%). Nonresponse bias was evident in both modes but, with the exception of age, was not differential between modes. The rate of missing responses was higher for mail than telephone respondents (1.59 vs. 0.49 missing items). Health ratings based on the SF-36 scales were less favorable, and reports of chronic conditions were more frequent, for mail than telephone respondents. Results are discussed in light of the trade-offs involved in choosing a survey methodology for health status assessment applications. Norms for mail and telephone versions of the SF-36 survey are provided for use in interpreting individual and group scores.