A funny thing has been happening. While Americans' income has skyrocketed in the past 50 years, levels of self-reported happiness have remained sadly steady. And consider this: On a life satisfaction scale from 1 to 7, Calcutta slum dwellers put themselves at 4.6, while Forbes magazine's "richest Americans" rate themselves only a 5.8. Such existential calculus has encouraged economists and psychologists to join forces in the white-hot field of behavioral economics. It's also leading them to assess the precise contribution of quality-of-life elements to our sense of prosperity. Along with such traditional variables as employment rates and income, there's a growing recognition that mental health, satisfaction with work and political freedom figure powerfully into measures of societal well-being.