Use of multiple causes of death in the analysis of occupational cohorts--an example from the oil industry.

OBJECTIVES To examine the efficacy of routine examination of multiple causes of death occurring on death certificates in cohort studies, with an example from the oil industry. METHODS The underlying and multiple causes were coded for all notified deaths from a cohort of 35,000 men employed at eight oil refineries in the United Kingdom. Matrices of the frequencies of underlying causes by contributory causes were analysed for the total population and by subgroups defined by refinery, occupation, age, and calendar period of death. RESULTS Over 75% of the 10,128 certificates had two or more causes but this varied by disease. Many ratios of mentions of total to underlying causes were similar to those of England and Wales. Ratios for cancer of the larynx and pneumonia were lower, indicating possible over-reporting of these diseases as the underlying cause. Investigation of an excess of pneumonia deaths at one refinery indicated possible miscoding of the underlying cause or the wrong position of pneumonia on some certificates, particularly in combination with malignancy and stroke. CONCLUSIONS Routine analysis of multiple causes of death can provide useful additional information in cohort studies.