The researchers, from the University of Virginia, the University of Illinois and Michigan State University, looked at data from the World Values Survey, a large-scale analysis of economic, social, political and religious influences around the world. They also analyzed the behaviors and attitudes of 193 undergraduate students at Illinois.

Their findings challenge the common assumption that all measures of well-being go up as happiness increases. While many indicators of success and well-being do correspond to higher levels of happiness, the researchers report, those at the uppermost end of the happiness scale (people who report that they are 10s on a 10-point life satisfaction score) are in some measures worse off than their slightly less elated counterparts.

To put the findings in perspective, it is important to note that happiness generally correlates with all kinds of positive measures, said Illinois psychology professor Ed Diener, an author of the study. In general, the happier you are the more successful you are in terms of money, employment and relationships.

"Happy people are more likely (than unhappy people) to get married, are more likely to stay married, are more likely to think their marriage is good," Diener said. "They're more likely to volunteer. They're more likely to be rated highly by their supervisor and they're more likely to make more money."

Happy people are also, on average, healthier than unhappy people and they live longer, Diener said. And, he said, some research indicates that happiness is a cause of these sources of good fortune, not just a result.

"But there is a caveat, and that is to say: Do you then have to be happier and happier" How happy is happy enough?"

The research team began with the prediction that mildly happy people (those who classify themselves as eights and nines on the 10-point life satisfaction scale) may be more successful in some realms than those who consider themselves 10s. This prediction was based on the idea that profoundly happy people may be less inclined to alter their behavior or adjust to external changes even when such flexibility offers an advantage.

Their analysis of World Values Survey data affirmed that prediction.

"The highest levels of income, education and political participation were reported not by the most satisfied individuals (10 on the 10-point scale)," the authors wrote, "but by moderately satisfied individuals (8 or 9 on the 10-point scale)."

The 10s earned significantly less money than the eights and nines. Their educational achievements and political engagement were also significantly lower than their moderately happy and happy-but-not-blissful counterparts.

In the more social realms, however, the 10s were the most successful, engaging more often in volunteer activities and maintaining more stable relationships.

The student study revealed a similar pattern in measures of academic and social success. In this analysis, students were categorized as unhappy, slightly happy, moderately happy, happy or very happy. Success in the categories related to academic achievement (grade-point average, class attendance) and conscientiousness increased as happiness increased, but dropped a bit for the individuals classified as very happy. In other words, the happy group outperformed even the very happy in grade-point average, attendance and conscientiousness.

Those classified as very happy scored significantly higher on things like gregariousness, close friendships, self-confidence, energy and time spent dating.

The data indicate that happiness may need to be moderated for success in some areas of life, such as income, conscientiousness and career, Diener said.

"The people in our study who are the most successful in terms of things like income are mildly happy most of the time," he said.

In an upcoming book on the science of well-being, Diener notes that being elated all the time is not always good for one's success -- or even for one's health. Reviews of studies linking health and emotions show that for people who have been diagnosed with serious illnesses, being extremely happy doesn't always improve survival rates, Diener said. This may be because the elated don't worry enough about issues that can have profound implications for their ability to survive their illness, he said.

"Happy people tend to be optimistic and this might lead them to take their symptoms too lightly, seek treatment too slowly, or follow their physician's orders in a half-hearted way," he writes.

All in all, Diener said, the evidence indicates that happiness is a worthy goal for those who lack it, but the endless pursuit of even more happiness for the already happy may be counterproductive.

"If you're worried about success in life, don't be a 1, 2, 3 or 4 (on the 10-point scale)," Diener said. "If you are unhappy or only slightly happy, you may need to seek help or read those self-help books or do something to make yourself happier. But if you're a 7 or 8, maybe you're happy enough!"

This research was published in the December 2007 Perspectives on Psychological Science.

Note: If no author is given, the source is cited instead.

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