The summary of the study the article mentions and links to doesn't show if the trend is an average of some sort or if it's the result of a more self-selecting s

The summary of the study the article mentions and links to doesn't show if the trend is an average of some sort or if it's the result of a more self-selecting sample region. Unfortunately between that and only having first-hand local culture knowledge, I am unqualified to speculate in a meaningful way about the differences in culture and environment. Also, just because a trend is increasing does not also mean that there's an underlying masking effect or that there isn't overall convergence. Ideally at least similar studies would be performed on a global basis if a global comparison is occurring.