ASSESSMENT OF OCCUPATIONAL EXPOSURE IN A POPULATION-BASED CASE-CONTROL STUDY - COMPARING POSTAL QUESTIONNAIRES WITH PERSONAL INTERVIEWS

Background--In case-control studies, data collection on occupational e xposures by means of personal interviews is usually costly and time co nsuming. As detailed semiquantitative information on exposure from the se interviews often has to be dichotomised in the analyses due to the small numbers of exposed subjects, the question is raised whether simp le postal questionnaires yield the same results for occupational expos ure in epidemiological studies as job specific personal interviews. Me thods--Data on occupational exposures during pregnancy were compared f rom 121 women who both completed a checklist with 17 occupational expo sure categories in a postal questionnaire and were personally intervie wed with specific questions on exposure with details of job and task. kappa Coefficients were calculated as measures of agreement corrected for chance, and sensitivity and positive predictive values as measures of validity and usefulness, with the exposure assessment based on inf ormation from the interview as the gold standard. Results--Values of k appa varied from 0.09 for domestic cleaning agents to 0.70 for pestici des, indicating only low to moderate agreement between the questionnai re and the interview. Sensitivity ranged from 38% to 100%, with the hi ghest values for agents used by healthcare workers. Positive predictiv e values were lower, between 9% and 63%, which indicates that overrepo rting was more common than underreporting in the questionnaire. Conclu sions--These results underline the high potential for misclassificatio n of occupational exposure in studies based on questionnaires. Therefo re, postal questionnaires are not considered an alternative to job and task specific personal interviews in epidemiological studies.