Observations that MS is more common in the Northern latitudes of Europe and North America were originally interpreted as showing a latitude effect, the so-called North–South gradient. Recent evidence suggests that this may be an artifact that caused immigration patterns. Emigrating Northern (European) peoples originally settled in northern latitudes in America that more closely resembled their homelands.
It has been found that veterans with Scandinavian surnames living in the northern United States have the same risk of MS as those who live in the South. In the past, few neurologists lived in the southern United States. This was and still is true in areas of Australia. Because a diagnosis is not accepted unless made by a neurologist, it is obviously made less commonly in underserved areas such as northern Australia and, at least in the past, the southern United States.