Contrary to those several studies telling us, counter-intuitively, that people aren't made happier by increased economic well-being, there's a report of one study here that puts this in question. Only, it's not economic development all on its own that makes people happier; other things come into it as well:
[A] group of researchers, citing data from 1981 to 2007, says... that happiness rose in 45 of the 52 countries for which extensive data was available, including the U.S., Japan, Spain, France, Germany and Britain.
Furthermore, the cause wasn't income but freedom.
In the researchers' words, "Since 1981, economic development, democratization, and increasing social tolerance have increased the extent to which people perceive that they have free choice, which in turn has led to higher levels of happiness around the world."
What a surprise! You might have thought lack of economic development, political repression, intolerance and lack of choice would really appeal to people and keep them cheery; but apparently not. There's also this, almost as a throwaway, and implicitly challenging a certain form of (narrow) liberalism: 'income increases freedom'. That's pretty obvious really, but according to a certain ideological defence of capitalist inequality, liberal capitalist societies maintain individual freedoms while accepting vast inequalities. What the above throwaway line concedes is that significant economic inequality amounts to a differential distribution of individual freedom.