If you’ve read any news in the last several years about happiness research, you may have been disappointed (or thrilled, depending on your current happiness) to learn that we’re destined to maintain the same level of general satisfaction throughout our lives, no matter what decisions we make. This hypothesis, called set-point theory, is also known as the "hedonic treadmill." However, a new long-term study of happiness contradicts that theory and suggests that happiness is related to our life choices and can change greatly over time.

An international team of researchers has published a paper in PNAS based on data from the German Socio-Economic Panel (SOEP). Since 1984, the SOEP has surveyed its participants every year, and currently collects yearly data from over 60,000 German respondents. While other long-term studies rely on data from only one person per household, the SOEP collects information from everyone living in the home. Once a family member moves out and begins their own household, their new family members become part of the survey.

The PNAS study used data from SOEP respondents aged 25 to 64, who, according to set-point theory, should be stuck on the hedonic treadmill. Every year, SOEP respondents are asked to assess their current life satisfaction on a scale of 1 to 10. Based on these scores, as well as several other questions, the researchers were able to determine that personal choices are associated with changes in life satisfaction over a period of many years.

Twenty years after the study started, nearly 40 percent of respondents had changed their satisfaction levels significantly, moving either up or down the happiness spectrum by at least 25 percentile. The researchers found that these changes were related to personal choices the respondents revealed in the survey. Five particular factors are particularly important: partner characteristics, life goals and priorities, religion, the gap between work and leisure time, and adoption of a social and healthy lifestyle.

From previous research, we already know that neurotic people are less happy in general. However, it turns out that choosing a neurotic partner is associated with decreased satisfaction in the long run. Interestingly, the similarity (or disparity) between your personality and your partner’s has no significant effect on happiness.

Personal priorities, however, are extremely important in determining someone’s satisfaction. Individuals that prioritize altruistic or family goals tend to be happier than those with selfish goals such as success and material goods. Your partner's priorities can also affect your satisfaction; women whose partners value family goals are much happier than those with partners who place a low priority on family.

Attending church is regularly associated with increased long-term life satisfaction, although the study did not directly measure the effect of religious beliefs on happiness.

The researchers found that one of the most important factors in happiness is the gap between the number of hours someone works per week and the amount of time they’d like to work per week. If that difference is three hours or less, an individual is likely to be quite happy. People who are overworked (that is, they work greater than three hours more per week than desired) are less satisfied, and those who are underworked tend to be the unhappiest of all. Beyond work, how people spend their time is also related to happiness: those who engaged in frequent social activities and exercise were also much happier than those that didn’t.

Set-point theory claims that, no matter what personal decisions you make, your level of satisfaction will not change much in the long term. The SOEP data shows that life choices such as who your partner is, what you prioritize, and how you spend your time, are tied to your happiness. More importantly, the study shows that your happiness can change over time if these choices change. The researchers acknowledge that there may be some “reverse causation” at work; while some of the changes in satisfaction are a result of personal choices, changes in general happiness may also affect choices. For example, increases in satisfaction may make it easier for people to exercise or spend time with friends.

From these results, it seems (thankfully) that we’re not confined to the hedonic treadmill for our entire lives. But remember the other implication of this research: some of the decisions we make every day may affect our long-term happiness in some way.

PNAS, 2010. DOI: 10.1073/pnas.1008612107 (About DOIs).