"Don't worry, be happy" may be more than just a wishful mantra. A new study finds that people's happiness levels can change substantially over their lifetimes, suggesting that happiness isn't predetermined by genes or personality.
Psychologists have long argued that people have a "set point" for happiness. Regardless of what life brings, the set-point theory goes, happiness levels tend to be stable. A big life event could create a boost of joy or a crush of sorrow, but within a few years, people return to a predetermined level of life satisfaction, according to the theory.
The new study, which used a nationally representative sample of almost 150,000 German adults, finds the opposite. People's long-term life satisfaction can change, the researchers report today (Oct. 4) in the Proceedings of the National Academy of Sciences. In fact, a substantial number of people followed over 25 years saw their happiness levels shift by one-third or more.
The study also echoed previous happiness research in finding that money doesn't buy happiness.
"People with a lot of money are more satisfied with their lives... but mainly due to the more interesting and challenging jobs they have," study author Gert Wagner, a researcher at the Max Planck Institute for Human Development in Germany, told LiveScience. "Money is simply a byproduct of good and satisfying jobs. If you want to be satisfied with your life, you must spend time with your friends and your family."
Wagner said that previous work suggests findings on happiness from one developed country, like Germany, should also hold true for another, such as the United States. In fact, a study in May found that in the United States, happiness tends to increase with age.
I'm happier than you
The researchers used data from a study of German adults spanning from 1984 to 2008. Each year, the participants answered questions on their life satisfaction, life goals and other measures like how much they exercise and socialize.
By averaging life-satisfaction responses to even out any short-term effects, the researchers plotted out the respondents' happiness by percentiles. Someone in the 99th percentile, for example, would be happier than 99 percent of the study participants.
People shifted in the rankings — and thus in their levels of happiness — quite a bit. Just over 38 percent changed their position in the distribution by 25 percentiles or more during the study period. About 25 percent changed by 33.3 percentiles or more, and 11.8 percent changed by 50 percentiles.
So what contributed to long-term happiness? The researchers found several correlations between life choices and life satisfaction:
* Marry well: The personality traits of partners influenced people's happiness. Neuroticism, or a tendency toward anxiety, emotional instability and depression, was most influential. People who married or partnered with neurotic people were less likely to be happy than people who married non-neurotic types.
* Focus on the family: People who assigned relatively high value to altruistic and family goals compared with career goals were happier. Women were also happier when their male partners ranked family goals high.
* Go to church: People who went to church more often were happier, though the study can't determine whether the happiness is related to religious views or to the social circle religious organizations offer.
* Work, but not too much (or too little): People's happiness matched how well they felt their work hours matched their desired work hours. In other words, people who worked more or fewer hours than they preferred were less happy. Working less or being unemployed was worse than working too much, presumably because underemployment is a financial blow, the researchers wrote.
* Get social, and get moving: Social interaction and exercise were both associated with happiness. Working out made people happier regardless of body weight. The only correlation between body weight and happiness was that underweight men and obese women were more likely to be unhappy.
Mysteries of happiness
"In its extreme form, set-point theory was never credible," Daniel Kahneman, an emeritus professor of psychology at Princeton University and the winner of the 2002 Nobel Prize in Economic Sciences, told LiveScience. "If it was taken to mean that the only factor that determines happiness or life satisfaction is genetic, so that people always come back to exactly to the same point, this was utterly incredible."
The current study is a "useful" demonstration that life changes can influence people's life satisfaction, said Kahneman, who was not involved in the research. However, the correlations between certain goals and traits and happiness doesn't necessarily answer the nature-versus-nurture question.
"They're suggesting that the goals are chosen. But the goals may be part of personality," and thus partially genetic, he said. "The fact that goals matter, like altruism and materialism, that really doesn't help us distinguish between personality and circumstances."
More studies are needed that track large populations of people after influential changes, like the enactment of new laws, said Andrew Oswald, a professor of behavioral science at the University of Warwick who studies happiness but was not involved in the current study. By comparing people who lived under, say, a new state tax law that affected income to those who lived in a nearby state without the law, researchers could begin to look at happiness in a more experimental way, he said.
"The key thing is that life events good and bad do shape happiness over long periods," Oswald said. "We are, in part, the product of our experiences. It's not all born into us."