EXPOSURE TO MAGNETIC-FIELDS ESTIMATED FROM LAST JOB HELD IN AN ELECTRICAL UTILITY IN QUEBEC, CANADA - A VALIDATION-STUDY

Objectives-To investigate how closely the variables of exposures to ma gnetic fields based on the last job held in an electrical utility in Q uebec, Canada, compared with those based on the workers' entire employ ment history with the company. Methods-In large cohort studies, the la st job held is often used to assign exposure to the study subjects. Ex posure was assigned in this way for a mortality study of a cohort of e lectrical utility workers in Quebec. For the present study, a sample o f the cohort was used to compare the exposure estimates obtained from the last job with those obtained from full work histories. Results-The correlations between indices based on the last job and on all jobs va ried between 0.75 and 0.78. The mean was slightly lower when only the last job was used. The last job was particularly good in identifying t he most highly exposed people (for the exposure cut off point of 90th percentile for the last job and for all jobs, sensitivity = 0.69, spec ificity = 0.97, kappa = 0.66). The results suggest that although not a ll workers starting in highly exposed jobs stayed in them, it seemed t hat the workers who ended their working life in highly exposed jobs ha d stayed in these jobs throughout their working Life.Conclusion-The re sults indicated some (but not catastrophic) loss of information when e stimates of exposure were based on the last job only.