People's happiness levels change with age, an idea reflected in personal experiences and public opinion polls, but a new study shows that much of that change may boil down to how people define happiness itself.

Whereas happiness in younger people is often related to excitement, for older people, contentment was associated with a happy existence, the researchers found.

The study indicates there are at least two different kinds of happiness, "one associated with peacefulness and one associated with being excited," study researcher Cassie Mogilner, a professor of marketing at Wharton, told LiveScience.

The difference appears to result from the importance placed on the future versus the present. Younger people, generally more concerned with the future, base their happiness more on excitement, the researchers found, while older people place a higher value on the present, and so contentment tends to be a greater source of happiness for them.

Measuring happiness

Mogilner and colleagues ran five studies involving different groups of people in their teens, 20s, 30s, 40s and 50s.

The researchers first examined blogs, using a computer program to look for words related to happiness and other emotions. (The tool used can be looked at online at wefeelfine.org.) These were analyzed along with the age and gender of the blogger. The tools were used on millions of blogs and the survey found about 70,000 expressions of happiness with enough data to include in the study.

The researchers also completed a survey to measure participants' definitions of happiness; and in another study, participants listened to a calm or energetic song and then indicated how they felt. In the fourth study, participants were read a passage discussing focusing on the present or a control tape. Afterward, participants were given a writing exercise. Younger participants were more likely to write about the present if they had heard that tape, while there was no effect in older participants.

Finally, participants were asked on what they would spend $100. Researchers coded those responses based on whether they were excitement-focused (for example, "a Nintendo Wii"), calming-focused (for example, "a bubble bath") or neither.

Despite the variation in studies, the results showed a fairly consistent shift in associations of happiness. For younger people, about 60 percent of happiness corresponded with levels of excitement, while for older people, 80 percent of happiness corresponded with levels of contentment. [5 Things That Will Make You Happier]

"I was incredibly impressed at the basic idea, how simple it is and how powerful the data were," said Brett Pelham, a program director in the social psychology program at the National Science Foundation.

Young at heart

The research would appear to extend even further than the study went, to young children, where excitement is an even bigger component of happiness, Pelham said. For a child, happiness is about excitement, like a trip to the zoo or a carnival. Just sitting around all day is not as much of a cheery experience for children. [7 Ways the Mind and Body Change With Age]

And perhaps hanging around a child could change an older adult's perception of happiness, placing more emphasis on excitement — in other words, perhaps spending time with the young can make you young at heart.

The results, which are detailed online in the journal Social Psychological and Personality Science, may explain why surveys and public polls of individuals' happiness have such varying results depending on participants' ages.

If the findings hold up with further study, something Pelham expects will happen, people's survey responses about their contentment or excitement one day should be predictive of their responses to questions about their happiness.

In the future, Pelham said, the framework of the study would allow for research into how happiness is impacted by gender or in different cultures.

And while individuals may vary in how much excitement or peacefulness affects their happiness, Mogilner said people should count on change.

"[People] should expect the things that make them happy and their experience of happiness to change," she said. "They should not be surprised or attribute these changes to life becoming less happy."

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