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HAPPINESS IS a state of mind, but if it were a place, it might well be the central American republic of Costa Rica. Located just a few hundred miles west of the benighted Haiti, Costa Rica is a corner of paradise here on Earth. Paradise, in this instance, doesn’t mean a Caribbean playground for idle millionaires, but rather, as defined by the 4.5 million people who actually make their lives there.

There are many ways of calculating the happiness of populations, but by any measure, Costa Rica is among the happiest places on Earth. The World Database of Happiness, compiled by Dutch sociologists, ranks it first among 148 countries surveyed, with a score of 8.5 from a possible 10 in how people “enjoy their life as a whole” (Ireland rates a respectable 7.6, though...