The Harvard Study of Adult Development

In the words of the study's long-time director George Vaillant, data can be boiled down to five words: "Happiness is love. Full stop." It's true: the one variable that predicted happiness in late life better than anything else was the number of so-called "warm relationships" the man had. That's true throughout his life, by the way — men who had warm relationships with their mother in childhood were found to earn an average of $87,000 more per year than others, and those who were close to their fathers showed higher satisfaction in late life. The study showed that it was actually relationships from around age 47 that proved to be the best predictors of happiness in the 80s and 90s.