Switzerland, Iceland, Denmark and Norway are the world's happiest countries, according to the 2015 World Happiness Report, which is put out by some influential economists. Three of these European states are not members of the European Union. What are they doing right that the rest of the world is doing wrong?

Jeffrey Sachs of Columbia University, Richard Layard of the London School of Economics and John Helliwell of the University of British Columbia have been putting out these reports since 2012. They are intended to remind governments that success is about more than economic growth and other such statistics. Sure, people are happier when they're richer and healthier, as they tend to be in more developed countries, but there are other contributors to perceptions of well-being. That's what the reports measures: People in various countries are asked how they perceive various aspects of their lives.

The report's authors say six variables account for three-quarters of the differences in happiness levels among countries: Gross domestic product per capita, social support, healthy life expectancy, freedom to make life choices, generosity and freedom from corruption. Two of these — social support and generosity — are relatively independent of economic development or the political system, which explains why some relatively poor, institutionally weak countries have happier populations than the strongest Western democracies. For example, Mexicans are happier than Americans, Brazilians enjoy higher perceived well-being than the residents of rich, free Luxembourg, and Venezuelans like their life better than Singaporeans.