Response to: 'Does 'job predict exposure to magnetic fields? by Sorahan and Swanson

We take the opportunity to reply to the letter to the editor by Sorahan and Swanson1 on our recent paper by Koeman et al.2 where we described a positive association between amyotrophic lateral sclerosis (ALS) and exposure to extremely low-frequency magnetic fields (ELF-MF) within a general population cohort study in the Netherlands. We argued that the described results strengthened the evidence suggesting a positive association between exposure to ELF-MF and risk of ALS mortality.

Sorahan and Swanson are correct to point out the importance of the quality of the exposure assessment when assessing the health effects of magnetic fields. We agree that a job-exposure matrix (JEM) is an imperfect method in assessing exposure as per design, it is not able to incorporate between-subject differences within a job title or between companies/worksites without having additional data on tasks and worksites. This will inherently result in some level of exposure misclassification....

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