> strong positive correlation between altitude and suicide rate (r = 0.50, p < 0.001).

That is not strong. Put differently, altitude only explains 25% of the suicide rate. I know some fields have lower thresholds for what they consider strong, but still. An effect, sure, but I'd bet on this pointing to something else.

Not familiar with the demographics vs geography here, but how do typical high-altitude places look like in terms of society? They control for median household income and population density, but what about social attitudes? (are these places more rural? more traditionalist?), number of ways people can engage socially (say, cultural events, clubs, and so on), does their diet differ? etc etc.

Also, maybe putting the year (2011) in the title might be good. There may be more recent work / reviews.

EDIT: I forgot to mention diet