The hedonic treadmill, also known as hedonic adaptation, is the supposed tendency of humans to quickly return to a relatively stable level of happiness despite major positive or negative events or life changes. According to this theory, as a person makes more money, expectations and desires rise in tandem, which results in no permanent gain in happiness. Brickman and Campbell coined the term in their essay "Hedonic Relativism and Planning the Good Society" (1971). During the late 1990s, the concept was modified by Michael Eysenck, a British psychologist, to become the current "hedonic treadmill theory" which compares the pursuit of happiness to a person on a treadmill, who has to keep working just to stay in the same place.
The Hedonic (or Happiness) Set Point has gained interest throughout the field of positive psychology where it has needed some revision. The theory has consequences for understanding happiness as both an individual and a societal goal.
The hedonic (or happiness) set point is a recently developed theory that requires further research. So far it illuminates an important facet of happiness and its homeostatic nature due to temperament. Less like a treadmill (which always tends towards one direction) and more like a thermostat (a negative feedback system), humans generally maintain a constant level of happiness throughout their lives—despite events that occur in their environment. The focus of positive psychology is to determine how to maintain or raise the hedonic set point.
Major theoretical approaches 
Behavioral/psychological approach 
Psychologists  have concluded that there seems to be a set hedonic level of happiness. While outside experiences may nudge our overall happiness upward or downward, we usually inexorably return to our set level of happiness. One major component in the behavioral and psychological approaches to hedonic set point is a concept referred to as the Hedonic Treadmill Model. This model is designed around psychologists' conjecture that good and bad events may alter our level of subjective happiness temporarily, but in the long run we adapt to changes in our lives from these experiences and our level of subjective happiness tends to adjust back to hedonic neutrality. Eysenck compared Brickman and Campbell’s idea of adaptation and the pursuit of happiness as a futile attempt, similarly to that of a person on a treadmill. A person can tirelessly work to get ahead, but they will always end up right back in the same place.
Brickman and Campbell originally concluded that everyone returns to the same neutral set point after a significantly emotional life event. Many years of research, however, have proven this detail of the hedonic treadmill theory to be simply untrue. Diener, Lucas, and Scollon concluded that people are not hedonically neutral, and that individuals have different set points which are, in part, determined by their temperament. They found that, for the most part, people generally tend to maintain a happy mood the majority of the time. However, in a study conducted by Mancini, Bonnano, and Clark, for example, people showed individual differences in how they responded to particular life events, such as divorce and widowhood. Diener, Lucas, and Scollon also concluded that individuals may have more than one happiness set point, such as a life satisfaction set point and a subjective well being set point, and that one's level of happiness is not just one given set point but can vary within a given range. In addition, researchers found that some individuals do experience substantial changes to their hedonic set point over time, though most others do not. Unlike the happiness set point, which can be relatively stable throughout the course of an individual’s life, the life satisfaction and subjective well being set points are a tad more complicated. In a longitudinal study conducted by Fujita and Diener (2005), it was found that the life satisfaction set point had somewhat of a “soft baseline”. This means that for most people, this baseline is similar to their happiness baseline. Their life satisfaction will hover around a set point for the majority of their lives and not dramatically change. For about a quarter of the population though, this set point is not stable, and does indeed move. As for the subjective well being set point, that is almost an entirely different story. Lucas (2007) wrote that long term data show that subjective well being set points do change over time, and that adaptation is not necessarily inevitable. Also, it is possible for someone’s subjective well-being set point to drastically change, in such cases as those individuals who acquire a severe, long term disability. However, as Diener, Lucas, and Scollon point out, the amount of fluctuation a person does around their set point is largely dependent on that individual’s ability to adapt.
Scientific approach 
Studies of happiness across several countries have begun in recent years, testing the true limits of our hedonic set point. Some studies attribute a large percentage of our happiness level to genetics. After following over a thousand sets of twins for 10 years, Lykken and Tellegen (1996) concluded that almost 50% of our happiness levels are determined by genetics. Headey and Wearing (1989) suggested that our position on the spectrum of the stable personality traits (neuroticism, extraversion, and openness to experience) is responsible for how to experience and perceive life events, indirectly also being responsible for our happiness levels.
Major empirical findings 
Lykken & Tellegen (1996) performed a 10-year, longitudinal, twin study and found that genetic factors have a significant impact on overall level of happiness, specifically that genetic factors may account for at least 44-52% of one's subjective well-being. They did so by administering subjective well-being questionnaires to a sample of 1,155 sets of identical and fraternal twins at the onset of the study, and then again 10 years later. After controlling for socioeconomic level, educational attainment, income, marital status, and religious commitment, they found a correlation of 0.44 - 0.52. This is a significant relationship, considering that fraternal twins' scores showed a correlation of less than 0.1. The researchers also found that the controlled demographic variables accounted for no more than 3% of the variance. Essentially, Lykken and Tellegen concluded that the variance in happiness observed in the sets of twins means that each individual’s happiness is almost equally determined by genetic factors and the experiences unique to each individual.
Diener & Fujita (2005) studied the stability of one's level of subjective well-being over time and found that for most people, there is a stable range in which their level of satisfaction varies. To measure the stability of one's level of well-being, they asked a panel of 3,608 German residents to rate their current and overall satisfaction with life on a scale of 0-10, once a year for seventeen-years. However, about one quarter of participants exhibited shifts in their level of life satisfaction over the course of the study, and 9% of participants experienced significant changes. They found that level of life satisfaction is more stable in the long run than it is in the short run, and that those with a higher mean level of life satisfaction also had more stable levels of life satisfaction compared to those with lower levels of satisfaction, who experienced more fluctuation in their levels of satisfaction throughout the course of the study.
Headey (2008) concluded that an internal locus of control along with "positive" personality traits (notably low neuroticism) are the largest significant factors affecting one's subjective well-being (SWB). The author also found that adopting "non-zero sum" goals, that is those which enrich one's relationships with others and with society as a whole (family-oriented and altruistic goals), increase the level of SWB. Conversely, attaching importance to zero-sum life goals: career success, wealth, and social status, will have a small but nevertheless statistically significant negative impact on people's overall subjective well-being (even though the size of a household's disposable income does have a small, positive impact on SWB). Duration of one's education seems to have no direct bearing on life satisfaction. And contradicting set point theory, there is apparently no return to homeostasis after sustaining a disability or developing a chronic illness. These disabling events are permanent, and thus according to cognitive model of depression, may contribute to depressive thoughts and increase neuroticism (another factor found by Headey to diminish SWB). In fact disability appears to be the single most important factor affecting human subjective well being. The impact of disability on SWB is almost twice as large as that of the second strongest factor affecting life satisfaction—the personality trait of neuroticism.
Although Headey (2008) concluded that there is apparently no return to a person’s overall happiness set point after sustaining a severe disability, a study conducted by Silver (1982) found contradicting results. For eight weeks, Silver followed accident victims who had sustained severe spinal cord injuries. About a week after their accident, Silver observed that the victims were experiencing much stronger negative emotions than positive ones. However, by the eighth and final week, the victims’ positive emotions actually outweighed their negative ones. The results of this study suggest that regardless of whether the life event is significantly negative or positive, people will generally always return to their happiness baseline.
Baumeister, Bratslavsky, Vohs, and Finkenauer (2001) performed a meta-analysis in which they looked at the impact of bad events in comparison to positive events in an individual’s life. They found that bad events had a greater impact psychologically on a person than positive events. A study carried out by Lucas, Clark, Georgellis, and Diener concurred with this finding. Although the study was focused on adaptation to changes in marital status, one of their largest findings was that widowhood has long lasting effects and not all widows experienced significant amounts of adaptation, while most married people did. While demonstrating that a negative life event can have a greater impact on a person’s psychological state and happiness set point than a positive event, this study also illustrated that the amount of adaptation that occurs is largely on an individual basis.
The concept of the happiness set point can be applied in clinical psychology to help patients return to their hedonic set point when negative events happen. Knowing that happiness can temporarily depart from one's given hedonic set point, determining when dips are occurring can be extremely helpful in treating conditions such as depression. When a dip occurs, clinical psychologists work with patients to recover from the depressive spell and return to their hedonic set point more quickly (one strategy is to provide patients with different altruistic activities that can help him or her return to their hedonic set point.). In doing this, psychologists are helping to equip patients with the tools to combat any potential depressive spells that may arise in the future.
Critical views 
One critical point made regarding our individual set point is to understand it may simply be a genetic tendency and not a completely determined criterion for happiness, and it can still be influenced.
The notion of "historical neglect", that people tend to focus more on negative emotions than positive emotions, can become a great detriment to improving our happiness set point. Negative emotions require more attention and are remembered better, overshadowing any positive experiences that may even outnumber negative experiences.
Ahmed and Koob (1998), in a study on moderate to excessive drug intake on rats, put forth that the use of mind-altering drugs such as cocaine can change an individual's hedonic set point; their study provides an animal model for the relation between excessive drug usage and how it affects our hedonic set point.
See also 
- Abolitionism (bioethics)
- Happiness economics
- Leisure satisfaction
- Paradox of hedonism
- Rosenbloom, Stephanie (August 7, 2010). "But Will It Make You Happy?". New York Times. Retrieved August 16, 2010.
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- Mancini, A; Bonnano, Clark (2011). "Stepping off the hedonic treadmill: Individual differences in response to major life events". Journal Of Individual Differences 32 (3): 144–152. doi:10.1027/1614-0001/a000047.
- Fujita; Diener (2005). "Life satisfaction set point: stability and change". Journal of Personality and Social Psychology 88 (1): 158.
- Lucas, R.E. (2007). "Adaptation and the Set-Point Model of Subjective Well-Being: Does Happiness Change After Major Life Events?". Directions In Psychological Science 16 (2): 75–79. doi:10.1111/j.1467-8721.2007.00479.x.
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- Headey; Wearing (1989). "Personality, life events and subjective well-being: Toward a dynamic equilibrium model". Journal of Personality and Social Psychology 57: 731–739.
- Headey, B. (2008). "Life Goals Matter to Happiness: A Revision of Set-Point Theory". Social Indicators Research. Vol. 86. No. 2, pp. 213
- Silver (1982). Coping with an undesirable life event: A study of early reactions to physical disability. Northwestern University.
- Baumeister; Bratslavsky, Vohs, Finkenauer (2001). "Bad is stronger than good". Review of General Psychology 5 (4): 323–370. doi:10.1037/1089-26188.8.131.523.
- Lucas; Clark, Georgellis, Diener (2003). "Reexamining adaptation and the set point model of happiness: Reactions to changes in marital status". Journal of Personality and Social Psychology 84 (3): 527–539. doi:10.1037/0022-35184.108.40.2067.
- "Psychologists now know what makes people happy" Marilyn Elias. New York Times. December 10, 2009.
- Sheldon, K. M.; Lyubomirsky, Sonja (2006). "Achieving Sustainable Gains in Happiness: Change Your Actions Not Your Circumstances". Journal of Happiness Studies 7: 55–86.
- Ahmed, S. H.“Transition from moderate to excessive drug intake: change in hedonic set point.” Science, Oct 9, 1998, Vol.282 (5387), p. 298
Further reading 
- The Overspent American: Why We Want What We Don't Need by Juliet B. Schor