Intelligent people might disagree on the right response to immigration, but the cause of it seems pretty clear. People move abroad to improve living conditions -- whether economic or political -- for themselves and their families. But what about those who are only somewhat dissatisfied with their lot in life? Apparently they stay home.

In a paper for the Journal of Happiness Studies, economists Nicole Simpson of Colgate University and Linnea Polgreen of the University of Iowa compared the emigration rates of 58 countries with their national happiness scores, as measured by the World Values Survey. What they found is that there's a roughly U-shaped relationship between happiness and emigration: The least happy countries, like Albania and Ukraine, have high emigration rates, but so do the world's happiest countries, like Colombia and El Salvador. Why? Extremely happy countries produce optimistic, confident people more likely to risk relocating overseas to improve their prospects. The rest, it seems, are stuck in the middle.