I thank Dr. Sajedi for the comment on our article,1 and for noting the interesting articles by Sajedi and colleagues.2–5 My colleagues and I have no explanation for the apparent drop in incidence of multiple sclerosis (MS) in Denmark in the 1960–1969 period, but we decided not to discuss any hypotheses that could not be tested by our data (or elsewhere). Countless factors confound the association between time or geography and MS. The way from covariation to causality is long, and a possible biological link between geomagnetic factors and MS remains inexplicable.

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