Approaches to Calculation of Average Exposure in Analysis of Epidemiologic Cohorts Using Large Acrylonitrile Cohort as an Example

Objectives: To explore two different approaches to calculate average exposure in occupational cohorts using a large occupational cohort as an example. The data for occupational cohort exposed to acrylonitrile was collected and analyzed previously by NCI; outcome was lung cancer. Methods: Both approaches use cumulative exposure as the numerator. As the denominator, one uses the duration of exposure, while the other uses the length of employment. The former approach is used when detailed exposure history is available, and the latter is used when exposure history is less detailed. The differences are investigated for a large occupational cohort. Results: With restricting the cohort to only those with enough latency for lung cancer, the cumulative exposure divided by the length of employment is a significant predictor of the lung cancer mortality, while cumulative exposure divided by the duration of exposure (average intensity) is not. Analysis is shown not to be positively confounded by smoking. Conclusion: Both approaches should be considered when calculating an average exposure metric.