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Koeman et al reported an association between amyotrophic lateral sclerosis and estimated exposure to extremely low-frequency magnetic fields (MF) from a cohort study in the Netherlands.1
The authors omitted to mention the most recent findings from a similarly powered cohort study from the UK electricity supply industry.2 The omission is unfortunate, not just because the UK study found no convincing associations, but also because consideration of the different exposure assessment methods used in these two studies highlights a weakness of the methods used in the Dutch study.
The Dutch study used a job-exposure matrix (JEM) to assess exposure, a modified version of the JEM published by Bowman et al in 2007.3 This latter paper highlighted …
Footnotes
Contributors Both authors drafted this letter by making multiple iterations.
Competing interests TS is Principal Investigator of a cohort mortality study of workers in the UK electricity supply industry and receives research funding from the Energy Networks Association (ENA), a trade association. JS is employed by National Grid and worked on this letter as part of his employment, but no approval was required or sought from anyone else in the Company.
Patient consent Not relevant. The letter does not concern human subjects, it is a comment on methodology.
Provenance and peer review Not commissioned; internally peer reviewed.