The richest countries in the world are generally the happiest:
The Gallup researchers found evidence of what many have long suspected: money does buy happiness--at least a certain kind of it. In a related report, they studied the reasons why countries with high gross domestic products won out for well-being, and found an association between life satisfaction and income.
But egalitarianism and social cohesion also make people happier:
"The Scandinavian countries do really well," says Jim Harter, a chief scientist at Gallup, which developed the poll. "One theory why is that they have their basic needs taken care of to a higher degree than other countries. When we look at all the data, those basic needs explain the relationship between income and well-being." ...
But there's more to happiness than riches. The Gallup study showed that while income undoubtedly influenced happiness, it did so for a particular kind of well-being--the kind one feels when reflecting on his or her own successes and prospects for the future. Day-to-day happiness is more likely to be associated with how well one's psychological and social needs are being met, and that's harder to achieve with a paycheck.
Take Costa Rica. The sixth-happiest country in the world, and the happiest country in the Americas, it beat out richer countries like the United States. That's because social networks in Costa Rica are tight, allowing individuals to feel happy with their lot, regardless of financial success.
I don't have much to add to this, except to note that these sorts of polls should always be taken with a grain of salt. But this is not the first happiness survey to show these two effects. The trick is figuring out how income growth is related to social cohesion and the welfare state.