In the roughly three decades that psychologists and economists have taken the idea of researching happiness seriously, and after the survey data analysis of hundreds of questionnaires, few facts have emerged: friendship, marriage, employment and good health boost happiness. Once people have enough money to cover the basics, wealth and happiness are poorly correlated.
So what determines happiness? Generally speaking, within countries, wealthy people are happier than the destitute, but after that the relationship is complicated. Once people make a certain amount of income, comparison effects start to kick in and then happiness depends not so much the wealth we enjoy, but how it compares to what our neighbors, co-workers or other members of our reference group have.
Cross-country studies of wealth and happiness are even more problematic. Cross-country research shows that on average wealthier countries are happier than destitute countries – but after that there's no linear relationship. People in Afghanistan are as happy as people in Latin America, even though objective conditions are worse in Afghanistan. Kenyans are as satisfied with their health care as Americans.
In addition, surveys of self-reported happiness don't measure people's ability to adapt to both pleasant and unpleasant conditions. For example, people tend to become accustomed to higher levels of crime. Assault or theft victims who live in higher-crime cities such as Lima, Peru, are less unhappy about crime than residents of a place like Wichita, Kansas. Peruvians aren't necessarily happier than Kansans about crime, they are just used to it. Or, put another way, they never had the opportunity to recognize they're not in Kansas anymore.
Moreover, the happiness comparisons don't account for the impact of social context. If people who are obese or unemployed live someplace where lots of people are obese and unemployed, they are less unhappy than overweight and jobless who live near skinny French women and successful CEOs.