by Patrick Appel
Danes tend to be healthy, married and active all contributing factors to happiness. But why, researchers wondered, are Danes happier than Finns and Swedes, who share many of these traits, not to mention a similar culture and climate? The answer is, in a word, expectations. Danes have low expectations and so “year after year they are pleasantly surprised to find out that not everything is rotten in the state of Denmark,” says James W. Vaupel, a demographer who has investigated Danish bliss.
Happiness studies are always more complicated than they appear (check out this piece by the Atlantic or the musings of Will Wilkinson for more in that vein), and I'm wary of anyone who purports to definitively determine causality on a national scale. There are also studies that show that religion correlates with happiness, so the evidence is mixed, and I'm not sure that the answer is knowable.
Update: I missed this old Will Wilkinson post where he addresses this question directly. Worth pondering.