Two things stand out: First, the curves all follow the same general U-shaped trajectory. Youth and old age are periods of relative happiness, while middle age is something of a rock bottom. Second, they generally agree that the bottom of that U hits some time in the early 50s. These similarities are even more remarkable given the differences in the underlying surveys, which were administered in different countries. They include the General Social Survey (54,000 American respondents), the European Social Survey (316,000 respondents in 32 European countries), the Understanding Society survey (416,000 respondents in Great Britain) and others.