Migration shows early encounter with risk factor

ProfG made a post about the output of school kids and found that they seem to have a reduced output compared to non-Msers.

Yes this is depressing, but the other part of the MS jigsaw is  if you look at the at who have were born in a low-risk area and moved to a high risk area like the UK. The answer appears to be move before 15 and you take the risk of birth place. Understanding MS means explaining the observations of MS.
This says we encounter the risk factor many years before MS is diagnosed