Healthy worker effects explain differences in internal and external comparisons in a rubber industry cohort study

In his letter, Professor Sorahan1 poses an important question about our paper,2 namely, whether the results indicate that occupational exposures to agents such as rubber dust, rubber fumes and nitrosamines in the rubber industry are associated with increased risk of mortality from cancers of the bladder, lung, stomach, oesophagus, prostate, larynx, brain, pancreas, liver, and lymphatic and haematopoietic tissue. Sorahan argues that causation does not seem to be warranted since results from …