Second-quartile stocks did best with an 11.2% compound annual return through January 2002, followed by the third quartile at 9.1%.

FORBES: Money & Investing

Economists reckoned the uplift in happiness at that time was equivalent to 60% of the increase in wellbeing people tend to experience when they cross the line of median income, from the third income quartile into the second one.

BBC: Going for the happiness gold