Andrew Shaner, Geoffrey Miller, Jim Mintz (2007)
Variation in the age at onset of a multifactorial disease often reflects variation in cause. Here we show a linear latitudinal gradient in the mean age at onset of schizophrenia in 13 northern hemisphere cities, ranging from 25 years old in Cali, Columbia (at 4° north) to 35 years old in Moscow, Russia (at 56° north). To our knowledge, this striking association has not been previously reported. We consider several explanations, including the effects of pathogen stress, natural selection, sexual selection, migration, life-history profiles, or some combination of these factors, and we propose a test of competing causal hypotheses.
[Later onsets of schizophrenia generally lead to better (social) outcomes than early onsets. - Other stats show different (earlier) ages of onset. But maybe these other stats use other criteria. E.g. occurrence of first negative symptoms.]