Utility of proxy versus index respondent information in a population-based case-control study of rapidly fatal cancers

PURPOSE: This work provides an empirical assessment of the usefulness of obtaining exposure data from proxy respondents. METHODS: Two independent case groups were formed in data from a population-based case-control study. One case set was derived from proxy respondents. The second case series was derived from respondents who self-reported. The second case group was matched to the proxy case group for age, cancer site, and sex. These data were compared with a control group for completeness of information and identifying heterogeneity of risk estimates for a variety of variables. Index cases and controls were matched to the 829 available proxy respondents for sex, age (5-year groups), and cancer site. RESULTS: Proxy respondents provided levels of complete information similar to index cases and controls for height and weight; occupational physical activity; consumption of coffee, alcohol, and cigarettes; and family history of cancer. Proxies had more missing responses for variables concerning recreational physical activity, clinical depression, age at first menstruation, use of oral contraceptives, and occupational exposure to pesticides. Polytomous logistic regression models found only a few examples of meaningful heterogeneity among all variables, limited to models for coffee consumption and cigarette smoking. CONCLUSIONS: Our data suggest that proxy respondents, especially parents and spouses, provide adequately complete information for many, but not all, exposures common in epidemiologic studies.