EFFECTS OF AGRICULTURAL WORK AND OTHER PROXY-DERIVED CASE-CONTROL DATA ON PARKINSONS-DISEASE RISK ESTIMATES

This study examined the effects on Parkinson's disease risk estimates of exposure misclassification in proxy-derived data on agricultural wo rk, pesticide use, rural living, well water drinking, head trauma, smo king, and family history of Parkinson's disease or essential tremor. T he data were collected in 1989 as part of a population-based case-cont rol study of Parkinson's disease in Calgary, Canada. Nondemented cases (n = 130) were selected from a case register of Calgary residents wit h neurologist-confirmed Parkinson's disease. For each case, two matche d (sex and age +/- 2.5 years) community controls were selected by rand om digit dialing. Forty cases and 77 controls were randomly selected a s index respondents. The cases, controls, and one proxy respondent (sp ouse or off spring) for each index respondent were interviewed using a structured questionnaire. The data were analyzed using conditional lo gistic regression. Incorporation of proxy-derived data for 30% of the cases or controls, or both, resulted in considerable misclassification of exposure for some variables and, in most cases, attenuation of the odds ratio. The results indicate that pooling dichotomously classifie d data derived in part from self- and proxy respondents may result in biased estimates of Parkinson's disease risk associated with agricultu ral, family history, and head trauma factors.