Beyond the Hedonic Treadmill: Revising the Adaptation Theory of Well-Being

Abstract

According to the hedonic treadmill model, good and bad events temporarily affect happiness, but people quickly adapt back to hedonic neutrality. The theory, which has gained widespread acceptance in recent years, implies that individual and societal efforts to increase happiness are doomed to failure. The recent empirical work outlined here indicates that 5 important revisions to the treadmill model are needed. First, individuals' set points are not hedonically neutral. Second, people have different set points, which are partly dependent on their temperaments. Third, a single person may have multiple happiness set points: Different components of well-being such as pleasant emotions, unpleasant emotions, and life satisfaction can move in different directions. Fourth, and perhaps most important, well-being set points can change under some conditions. Finally, individuals differ in their adaptation to events, with some individuals changing their set point and others not changing in reaction to some external event. These revisions offer hope for psychologists and policy-makers who aim to decrease human misery and increase happiness.

Full text

Beyond the Hedonic Treadmill
Revising the Adaptation Theory of Well-Being
Ed Diener University of Illinois at Urbana–Champaign
Richard E. Lucas Michigan State University
Christie Napa Scollon Texas Christian University
According to the hedonic treadmill model, good and bad
events temporarily affect happiness, but people quickly
adapt back to hedonic neutrality. The theory, which has
gained widespread acceptance in recent years, implies that
individual and societal efforts to increase happiness are
doomed to failure. The recent empirical work outlined here
indicates that 5 important revisions to the treadmill model
are needed. First, individuals’ set points are not hedoni-
cally neutral. Second, people have different set points,
which are partly dependent on their temperaments. Third,
a single person may have multiple happiness set points:
Different components of well-being such as pleasant emo-
tions, unpleasant emotions, and life satisfaction can move
in different directions. Fourth, and perhaps most impor-
tant, well-being set points can change under some condi-
tions. Finally, individuals differ in their adaptation to
events, with some individuals changing their set point and
others not changing in reaction to some external event.
These revisions offer hope for psychologists and policy-
makers who aim to decrease human misery and increase
happiness.
Keywords: coping, subjective well-being, life satisfaction,
adaptation, happiness
I
magine a world in which the poorest diseased beggar
with no family or friends is as happy as the healthy
billionaire who has a surfeit of close and supportive
relationships. Or imagine that individuals living in a cruel
dictatorship where crime, slavery, and inequality are ram-
pant are as satisfied with their lives as people living in a
stable democracy where crime is minimal. Finally, imagine
that no matter how much effort and care someone put into
being happy, the long-term effects were no different than if
he or she lived a profligate and dissolute life. Implausible?
These surprising visions are based on a widely accepted
model of subjective well-being. Brickman and Campbell
(1971) described a hedonic treadmill, in which processes
similar to sensory adaptation occur when people experience
emotional reactions to life events. Just as people’s noses
quickly adapt to many scents and smells thereafter disap-
pear from awareness, Brickman and Campbell suggested
that one’s emotion system adjusts to one’s current life
circumstances and that all reactions are relative to one’s
prior experience. Myers described adaptation as a key to
understanding happiness. In his popular book The Pursuit
of Happiness, David Myers (1992) wrote, “The point can-
not be overstated: Every desirable experience—passionate
love, a spiritual high, the pleasure of a new possession, the
exhilaration of success—is transitory” (p. 53).
In the original treadmill theory, Brickman and Camp-
bell (1971) proposed that people briefly react to good and
bad events, but in a short time they return to neutrality.
Thus, happiness and unhappiness are merely short-lived
reactions to changes in people’s circumstances. People
continue to pursue happiness because they incorrectly be-
lieve that greater happiness lies just around the corner in
the next goal accomplished, the next social relationship
obtained, or the next problem solved. Because new goals
continually capture one’s attention, one constantly strives
to be happy without realizing that in the long run such
efforts are futile.
The hedonic treadmill theory is built on an automatic
habituation model in which psychological systems react to
deviations from one’s current adaptation level (Helson,
1948, 1964). Automatic habituation processes are adaptive
because they allow constant stimuli to fade into the back-
ground. Thus, resources remain available to deal with novel
stimuli, which are most likely to require immediate atten-
tion (Fredrick & Loewenstein, 1999). The happiness sys-
tem is thus hypothesized to reflect changes in circum-
stances rather than the overall desirability of the
circumstances themselves. This idea was formalized by
Carver and Scheier (1990), who maintained that emotions
depend on the rate of change of important circumstances.
In 1978, Brickman, Coates, and Janoff-Bulman of-
fered initial empirical support for the treadmill model. In
studies that have become classics in the field, Brickman et
al. concluded that lottery winners were not happier than
nonwinners and that people with paraplegia were not sub-
stantially less happy than those who can walk. Although
the empirical support for hedonic adaptation was, in fact,
mixed, the studies captured the attention of psychologists.
The idea of hedonic adaptation was appealing because it
Ed Diener, Department of Psychology, University of Illinois at Urbana–
Champaign; Richard E. Lucas, Department of Psychology, Michigan State
University; Christie Napa Scollon, Department of Psychology, Texas
Christian University.
Correspondence concerning this article should be addressed to Ed
Diener, Department of Psychology, University of Illinois, 603 East Daniel
Street, Champaign, IL 61820. E-mail: ediener@uiuc.edu
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Copyright 2006 by the American Psychological Association 0003-066X/06/$12.00
Vol. 61, No. 4, 305–314 DOI: 10.1037/0003-066X.61.4.305

offered an explanation for the observation that people ap-
pear to be relatively stable in happiness despite changes in
fortune. In addition, the treadmill theory explained the
observation that people with substantial resources are
sometimes no happier than those with few resources and
that people with severe problems are sometimes quite
happy. Thus, the research of Brickman and colleagues
became central to the way many scientists understand
happiness.
We and many other psychologists readily accepted the
theory of adaptation because evidence frequently supported
the idea. External conditions are often weak correlates of
reports of happiness. For instance, all demographic vari-
ables taken together predict less than 20% of the variance
in happiness (Campbell, Converse, & Rodgers, 1976). Die-
ner, Sandvik, Seidlitz, and Diener (1993) found that in-
come and happiness in the United States correlate only .13,
and Diener, Wolsic, and Fujita (1995) similarly found that
objective physical attractiveness correlated at very low
levels with reports of well-being. Perhaps even more sur-
prising, Okun and George (1984) found that objective
health on average correlated only .08 with happiness, and
Feinman (1978) found that people who were blind did not
differ in happiness from those who were able to see.
In addition, longitudinal studies that tracked changes
in happiness over time provided more direct evidence that
adaptation can occur. For instance, Silver (1982) found that
individuals with spinal cord injuries reported strong nega-
tive emotions one week after their crippling accident. How-
ever, two months later, happiness was their strongest emo-
tion. Similarly, Suh, Diener, and Fujita (1996) found that
good and bad life events affected happiness only if they
occurred in the past two months. More distant past events
did not predict happiness (although many of the events they
studied were relatively mundane). Furthermore, in a num-
ber of studies, researchers have traced reactions to the
death of a spouse, and these studies show that emotional
reactions eventually rebound after this major life event
(e.g., Bonanno et al., 2002; Bonanno, Wortman, & Nesse,
2004; Lucas, Clark, Georgellis, & Diener, 2003). Thus,
parts of the hedonic treadmill model have received robust
empirical support (see Fredrick & Loewenstein, 1999, for a
review).
Our Research on Adaptation
Over the last decade, we and others have tested predictions
derived from the treadmill theory, and our findings suggest
that the model requires important modifications. Although
the revisions leave certain core features of the adaptation
model intact, our research reveals that the idea is in need of
an update. After reviewing these revisions, we describe the
important implications that they have for psychology.
Revision 1: Nonneutral Set Points
The original treadmill theory suggested that people return
to a neutral set point after an emotionally significant event.
However, decades of research show that this part of the
hedonic treadmill theory is wrong. Instead, most people are
happy most of the time (Diener & Diener, 1996). For
instance, Diener and Diener reviewed studies using a va-
riety of methods of assessment, and they concluded that
approximately three quarters of the samples they investi-
gated reported affect balance scores (positive moods and
emotions ⫺ negative moods and emotions) above neutral.
Similarly, Biswas-Diener, Vittersø, and Diener (2005)
found that even in such diverse populations as the Amish,
African Maasai, and Greenlandic Inughuit, most people are
above neutral in well-being. In the most recent World
Ed Diener
Richard E.
Lucas
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Values Survey (a large-scale survey in which the nations
with the largest populations are sampled using probability
methods; European Values Study Group & World Values
Survey Association, 2005), 80% of respondents said that
they were very or quite happy. Thus, if people adapt and
return to a baseline, it is a positive rather than neutral one.
A general tendency to experience positive emotions
may provide the motivation to explore one’s environment
and to approach new goals (Fredrickson, 1998). Lyubomir-
sky, King, and Diener (2005) showed that positive moods
facilitate a variety of approach behaviors and positive out-
comes. Thus, the ubiquity of a positive emotional set point,
in concert with the less frequent experience of unpleasant
emotions, likely results from the adaptive nature of fre-
quent positive emotions.
Revision 2: Individual Set Points
The empirical research that has been conducted since the
publication of Brickman and Campbell (1971) reveals that
if people do have set points, they vary considerably across
individuals. These individual differences are due, at least in
part, to inborn, personality-based influences (Diener &
Lucas, 1999). Support for this view comes from at least
three different lines of research. First, research consistently
shows that one’s level of well-being is reasonably stable
over time (e.g., Eid & Diener, 2004). Second, behavioral
genetic studies show that well-being is moderately herita-
ble. For instance, Tellegen et al. (1988) found that identical
twins reared apart were much more similar in their levels of
well-being than were dizygotic twins who were reared
apart. Finally, research shows that personality factors are
strong correlates of well-being variables. Whereas any sin-
gle demographic factor typically correlates less than .20
(usually much less) with well-being reports, both self- and
non–self-report measures of personality tend to correlate
much more strongly with well-being (see Diener & Lucas,
1999, for a review). Thus, personality factors may predis-
pose individuals to experience different levels of
well-being.
Revision 3: Multiple Set Points
The idea of a happiness set point implies that well-being is
a single entity with a single baseline. However, work by
Lucas, Diener, and Suh (1996) indicates that the global
category of happiness is composed of separable well-being
variables. It is important to note that these variables some-
times move in different directions over time. Thus, the idea
of a unitary set point is not tenable, because positive and
negative emotions might both decline in tandem or life
satisfaction might move upward while positive emotions
decrease.
In Figure 1, we present age trends in positive affect,
negative affect, and life satisfaction from the first wave of
the Victoria Quality of Life Panel Study (see Headey &
Wearing, 1989, 1992; Scollon, 2004) and from the 1990
World Value Survey (Inglehart & Klingemann, 2000).
Both studies are based on probability samples, the former
from the state of Victoria in Australia and the latter from 42
nations around the world. As can be seen in this figure,
there were significant age effects for all five variables (all
ps ⬍ .001). However, these effects varied for the different
well-being variables. For instance, at the same point in the
life span that positive affect was declining (representing a
decrease in overall well-being), negative affect also de-
clined (representing an increase in overall well-being).
During this same period, both work and home satisfaction
increased. These data indicate that (a) there is not a con-
stant global happiness set point that remains stable over the
course of the entire life span and (b) “happiness” is not a
unitary concept with a single set point to which people
adapt. Instead, these findings suggest that different forms of
well-being can move in different directions (also see East-
erlin, 2005).
We also used the longitudinal component of the Vic-
toria Quality of Life Panel Study to examine change in
well-being within persons over time. Specifically, we mod-
eled change in work satisfaction and marital satisfaction
over an eight-year period using growth curve modeling.
Significant individual differences in change emerged on
both variables, indicating that different people changed at
different rates and in different directions (Scollon & Die-
ner, 2005). It is important to note that the correlation
between changes in the two variables was substantially less
than 1 (r ⫽ .48), even at the latent level. This shows that
the two variables do not always change in unison. Not all
individuals who increased in work satisfaction increased in
marital satisfaction. At best, only one quarter of the vari-
ance in change could be accounted for by the correspond-
ing amounts of change in another variable. Thus, not only
do the various well-being components change in different
ways over the course of the life span, but changes in one
domain do not fully correspond to changes in other
domains.
Christie Napa
Scollon
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As a final test of the separability of well-being com-
ponents, we examined the stability of positive and negative
affect over time in the Victoria Quality of Life Panel Study.
We found that, consistent with the idea that there is no
single set point, the various components exhibited differ-
ential stability. Specifically, long-term levels of negative
affect were substantially more stable than were long-term
levels of positive affect. In addition, the stability of positive
affect and life satisfaction declined with longer time peri-
ods, whereas the stability of negative affect did not (see
Table 1). These findings suggest that stable individual
baselines might be more characteristic of negative affect
than positive affect. However, over a period of a few years,
life satisfaction was most stable.
Revision 4: Happiness Can Change
Perhaps the most controversial aspect of Brickman and
Campbell’s (1971) hedonic treadmill model is the idea that
people cannot do much to change their long-term levels of
happiness and life satisfaction. If the hedonic treadmill
model is correct, adaptation is inevitable, and no change in
life circumstance should ever lead to lasting changes in
happiness. Although the work cited at the beginning of this
article was suggestive of such an effect, until recently very
little evidence has been available to provide longitudinal
tests of this hypothesis. Thus, questions have remained
about the extent to which important life events can perma-
nently alter individuals’ happiness set points.
One type of evidence demonstrating that life circum-
stances matter comes from well-being differences across
nations. If there are strong national differences in well-
being and these differences can be predicted from objective
characteristics of those nations, then this would suggest
that the stable external circumstances that vary across na-
tions have a lasting impact on happiness. The first column
of Table 2 presents affect balance scores (reported between
1981 and 1984) for several nations that differed markedly
in affluence and human rights. The right column of Table 2
Figure 1
Age Trends in Subjective Well-Being
Note. WVS ⫽ 1990 World Value Survey; VQOL ⫽ first wave of the Victoria Quality of Life Panel Study.
Table 1
Stability of Subjective Well-Being Measures in the
Victoria Quality of Life Panel Study and the German
Socio-Economic Panel Study
Time period between
measurements
Positive
affect
a
Negative
affect
a
Life
satisfaction
a
Life
satisfaction
b
2 years .37 .44 .61 .51
4 years .32 .40 .50 .45
6 years .32 .42 .44 .41
8 years .23 .48 .43 .37
a
Data are from the Victoria Quality of Life Panel Study.
b
Data are from the
German Socio-Economic Panel Study.
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shows that these nations also differed in life satisfaction.
Because the objective conditions in these countries re-
mained consistent for many years, the cross-national dif-
ferences in happiness suggest that people do not always
completely adapt to conditions. Perhaps more important,
these mean-level differences can be predicted from objec-
tive characteristics of the nations. For instance, Diener,
Diener, and Diener (1995) found that the wealth and the
human rights of nations were strong predictors of average
national well-being. Similarly, researchers at The Econo-
mist found that 85% of the variance in national levels of
well-being could be explained by nine objective character-
istics, including gross domestic product per person, life
expectancy at birth, political stability, and divorce rates
(Economist Intelligence Unit, 2005). Furthermore, if peo-
ple adapted to conditions, only change in conditions and
not the long-term level of conditions would influence feel-
ings of well-being. However, Diener and Biswas-Diener
(2002) reviewed studies showing that national levels of
wealth strongly predict the subjective well-being of na-
tions, whereas change in wealth is inconsistent in its effects
across studies.
This cross-sectional evidence that circumstances mat-
ter is supported by more definitive longitudinal studies
examining individuals over time. For instance, Fujita and
Diener (2005) used longitudinal data to determine whether
long-term average levels of happiness ever change. They
examined changes in baseline levels of well-being over a
17-year period in a large and representative sample from
Germany. Although there was considerable stability in
happiness reports, 24% of respondents changed signifi-
cantly from their early baseline, comprising the first five
years of the study, to the last five years. Nine percent
changed by approximately two standard deviations or
more. Thus, long-term levels of happiness do change for
some individuals. The more intriguing question, then, is
why happiness set points change for some individuals more
than for others.
Using the same sample of Germans, we have exam-
ined the ways that specific life events influence happiness.
In support of the initial adaptation model, people do seem
to adapt to some life events. For instance, Lucas et al.
(2003) showed that, on average, Germans did not get
lasting boosts in happiness after marriage. Instead, they
reported short-term increases in happiness that were fol-
lowed by relatively quick adaptation. However, the extent
of adaptation varies for different life events. Lucas et al.
(2003) showed that widows and widowers, people who
were laid off from work (Lucas, Clark, Georgellis, &
Diener, 2004), and individuals who divorced (Lucas,
2005b) all reported long-lasting changes in life satisfaction
after these life events. The widows showed the greatest
amount of adaptation (at least in terms of the absolute
increase from their lowest level of happiness), but even this
took about eight years and was not quite complete. Figure
2 shows life satisfaction levels before and after these four
important life events.
Together these results suggest that happiness can and
does change. What then should be made of the classic
empirical findings of Brickman et al. (1978)? First, it
should be noted that when Brickman et al.’s results are
examined closely, the evidence for adaptation is not nearly
as strong as many psychologists have tended to assume. In
the case of individuals with spinal cord injuries, Brickman
et al. did find that the participants who were disabled
reported significantly less happiness than did controls. In
fact, when we calculated standardized mean differences in
general happiness from Brickman et al.’s data, we found
that the difference between the spinal cord–injured and
control groups was about 0.75 standard deviations—an
effect that most psychologists would consider large. Sim-
ilar effects have been found numerous times: Authors of a
number of recent reviews have concluded that individuals
with spinal cord injuries are less happy than are people in
the general population, with effect sizes in the moderate to
large range (Dijkers, 1997, 2005; Hammell, 2004). How-
ever, the studies cited in these reviews are often published
in rehabilitation journals and are rarely cited in psycholog-
ical literature on adaptation.
Finally, Lucas (2005a) used two large, nationally rep-
resentative panel studies to examine adaptation to the onset
of disability. Participants in this study (who were followed
for an average of seven years before and seven years after
onset) reported moderate to large drops in satisfaction and
very little evidence of adaptation over time. For instance,
those individuals who were certified as being 100% dis-
abled reported life satisfaction scores that were 1.20 stan-
dard deviations lower than their nondisabled baseline lev-
els. Thus, although people with paraplegia and other
individuals with disabilities usually are not subjectively
miserable, happiness levels do seem to be strongly affected
by this important life circumstance. When compared with
the actual variability between individuals in happiness
rather than with the extreme endpoints of the scale, many
of the group differences in happiness are substantial.
Table 2
The Happiness of Selected Nations
Nation
Affect balance (PA ⫺ NA),
1981–1984
Life satisfaction,
1999–2001
Canada 2.33 7.85
United States 2.23 7.66
China 1.46 6.53
West Germany 1.45 7.42
Mexico 1.38 8.14
India 0.72 5.14
Turkey 0.62 5.61
Russia 0.33 4.65
Note. Mean scores are taken from the World Value Survey, the Bradburn
Affect Balance Scale, where affect balance can vary from 5 to ⫺5, with 0 as the
neutral point. The national differences in both positive affect (PA) and negative
affect (NA) in the full sample are highly significant, p ⬍ .001. Life satisfaction
scores, with a range of 1 to 10, were taken from the European Values Study
Group and World Values Survey Association (2005) Data Wave 1999 –2001.
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It should no longer come as a surprise that people
living in negative circumstances report well-being scores
that are above neutral. This well-documented fact is inter-
esting and theoretically important, but it should not be used
as evidence that people inevitably adapt. Furthermore, it is
not enough for researchers interested in adaptation to show
that people who have experienced a negative life circum-
stance report well-being scores that are higher than what
other people would think they should report (e.g., Brick-
man et al., 1978; Riis et al., 2005). Such research findings
tell more about the average person’s affective forecasting
errors than about adaptation itself (Gilbert & Wilson,
2000). To determine whether adaptation has occurred, it is
necessary to compare individuals who have experienced an
event or life circumstance with those who have not, ideally
following the same individuals over time.
Revision 5: Individual Differences in
Adaptation
An implicit assumption of the hedonic treadmill theory is
that adaptation to circumstances occurs in similar ways for
all individuals. If adaptation results from automatic and
inevitable homeostatic processes, then all individuals
should return to neutrality or at least to their own unique
baseline. But we have found individual differences in the
rate and extent of adaptation that occurs even to the same
event. In our longitudinal studies, the size and even the
direction of the change in life satisfaction varied consider-
ably across individuals. For example, Lucas et al. (2003)
found adaptation to marriage at the aggregate level, but
there was a great deal of variability in these effects. Indi-
viduals who reacted most positively to their marriage
tended to be above their baseline many years after the
event, but these individuals were counterbalanced by those
who experienced a lasting decline in satisfaction after their
marriage. In fact, the standard deviation for the amount of
change that occurred after the event was almost as large as
the standard deviation for baseline levels.
Understanding individual differences in adaptation
will help illuminate when and why adaptation does or does
not occur. For example, in our study on reaction and
adaptation to marriage (Lucas et al., 2003), we relied on
laboratory studies of emotional reactivity (e.g., Larsen &
Ketelaar, 1991) to predict that the happiest individuals
should react most strongly to positive life events. However,
the results showed—somewhat surprisingly—that less sat-
isfied individuals were more likely to benefit from marriage
in the long run. These individuals with initially low base-
lines reported more positive reactions to marriage, and
these positive reactions persisted long into the marriage.
One explanation for this effect is that the most satisfied
individuals are more likely than less satisfied individuals to
have strong social support even before the marriage. People
who chronically experience many positive events may have
Figure 2
Adaptation to Good and Bad Events
5.5
6
6.5
7
7.5
8
-5 -4 -3 -2 -1 0 1 2 3 4 5
Year
Life Satisfact
ion
Widowhood Divorce Unemployment Marriage
Year of Event
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less to gain from one more positive event. Likewise, people
who chronically experience many bad events may not be
strongly affected by the addition of one more negative life
event. Therefore, deviations from a person’s typical life
events might produce the greatest changes in happiness set
points (Headey & Wearing, 1992; Oishi, Diener, Choi,
Kim-Prieto, & Choi, 2005).
Two important research traditions shed light on when
people adapt or do not adapt to negative events. The first of
these traditions focuses on the utility of specific coping
strategies. The second focuses on personality characteris-
tics that influence the specific coping strategies that people
use. From these literatures, it is known that certain coping
strategies are more effective than others and that individ-
uals vary in their preferred strategies. For example, indi-
viduals who tend to use reappraisal strategies experience
more positive emotions and fewer negative emotions than
do individuals who use strategies such as suppression
(Gross & John, 2003). Using reappraisal is also associated
with having better interpersonal relationships, which are
likely to translate into increased social support. Similarly,
among older people, the endorsement of coping styles such
as using humor, seeking information, and “keeping going”
predicts adjustment to old age (Staudinger & Fleeson,
1996).
Personality researchers have shown that a number of
stable individual differences predispose people to use cer-
tain coping strategies (Carver, Scheier, & Weintraub,
1989). For example, neurotic individuals often choose in-
effective strategies for coping, which can lead to greater
reactivity to a stressful event (Bolger & Zuckerman, 1995)
and possibly a slower return to baseline levels of happiness.
Similarly, Ferguson (2001) found that neuroticism and
introversion were associated with relatively ineffective
coping behaviors such as denial. However, optimistic in-
dividuals tend to engage in active coping or strategies that
can actually change the situation that is causing negative
affect (Aspinwall & Taylor, 1997; Chang, 1998; Scheier,
Weintraub, & Carver, 1986). Such strategies often pay off
by leading to a resolution of the stressful situation. Opti-
mistic people also tend to seek out social support, engage in
positive reappraisal of adverse events, and feel as if they
have the resources to overcome stressful situations (Scheier
et al., 1986)—all factors that help buffer against the long-
term effects of negative life circumstances. For example,
optimism has been shown to predict problem-focused cop-
ing and quicker recovery from surgery (Scheier et al.,
2003). Thus, there appear to be individual differences in
effective coping and adaptation to stressful events.
Research on individual differences in adaptation raises
questions about the processes that underlie adaptation ef-
fects. If adaptation is an inevitable and automatic process,
it should occur in similar ways for most people, much as
homeostatic processes work to return all people to their
body temperature set point. The fact that substantial indi-
vidual differences in these effects exist argues against this
type of inevitable habituation model. It also suggests that
research into these individual differences may help psy-
chologists understand exactly how adaptation occurs. How-
ever, at this point, it is unclear whether there is a relatively
automatic core habituation process that can be modified by
coping and other variables or whether adaptation and cop-
ing are synonymous. Future research must incorporate
measures of coping (along with other potential moderators
and process variables) into sophisticated longitudinal stud-
ies that allow for strict tests of adaptation effects.
Recent research has provided a much stronger test of
the hedonic treadmill than earlier studies did because of
methodological refinements. First and most important, by
relying on very large samples, researchers in recent studies
have been able to track individuals from before an event
happens to the time of the event to many years after the
event. By contrast, earlier researchers drew conclusions
from cross-sectional data in which preevent levels of life
satisfaction of groups such as lottery winners or people
with paraplegia were unknown. Second, large longitudinal
designs allow for more precise measurement of changes in
happiness over time and more powerful statistical methods
that go beyond examinations of group means to reveal
individual differences in adaptation. Finally, recent studies
have used large and often representative samples of partic-
ipants, unlike early studies that frequently used small ac-
cidental samples.
Implications of the Revised Model
If revisions must be made to the original hedonic treadmill
model, is adaptation still an important concept for psycho-
logical research? We answer with a resounding “yes.”
Although recent studies have challenged the idea that ad-
aptation is inevitable, people do adapt to many life events,
and they often do so within a relatively short period of
time. Thus, adaptation processes can explain why many
factors often have only small influences on happiness.
People tend to adapt to these conditions over time.
However, recent findings do place limits on the types
of psychological processes that can account for the adap-
tation that does occur. For instance, initial models that
relied on automatic physiological systems to account for
hedonic adaptation will likely not be able to fully account
for all existing data. Instead, more flexible processes are
likely involved, and these processes may vary across events
and individuals or even within the same individual over
time. The research on coping with adversity will be a useful
starting point for investigations of adaptation. However,
processes related to adaptation to positive events must also
be explored.
Newer theories of adaptation (e.g., Kahneman & Tha-
ler, in press; Wilson & Gilbert, 2005) rely on individuals’
attention to particular life circumstances in explaining the
changes. Kahneman and Thaler, for instance, posited that
various features of a specific life circumstance might in-
fluence whether it draws a person’s attention. It is this
attention that determines whether an individual can adapt.
Thus, Kahneman and Thaler predicted that conditions that
continue to draw attention can influence well-being but that
the novelty of certain circumstances wears off and there-
fore they draw less attention over time. Wilson and Gilbert
further suggested that people naturally seek to explain and
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make sense of life events and circumstances. Features of
one’s life that cannot be explained continue to draw atten-
tion and thereby affect one’s emotions and overall well-
being. Experience-sampling reports over time of the stimuli
to which people attend are needed to test attention theories.
Whether these attention theories can predict greater and
less habituation has not yet been rigorously tested.
Our revisions to the hedonic treadmill model suggest
that interventions to increase happiness can be effective,
and research supports this conclusion. These changes might
be targeted at the individual, organizational, or even soci-
etal level. For instance, in an early set of studies, Fordyce
(1977, 1983) demonstrated in seminal studies that a mul-
tipronged program successfully raised individuals’ happi-
ness for an extended period of time. These gains in well-
being persisted over a period of a year or more. Perhaps
because of the widely accepted view that happiness could
not be changed, however, few rigorous studies have been
conducted to follow up on this work. Very recently, this has
begun to change. For instance, Sheldon and Lyubomirsky
(2004) demonstrated that changes in activities raised peo-
ple’s happiness. They found that when individuals per-
formed several random acts of kindness on one day each
week, their happiness improved. Seligman, Steen, Park,
and Peterson (2005) reported a series of happiness inter-
ventions that were implemented via the Internet. They
found that several of these interventions led to changes in
happiness that persisted for at least six months. Finally,
Emmons and McCullough (2003) found that interventions
to increase thoughts of gratitude increased levels of posi-
tive affect. Although these experimental intervention stud-
ies are in the initial stages, they indicate that levels of
happiness can be raised. Again, this contradicts the idea of
an unchangeable baseline for happiness.
If interventions can cause lasting changes among in-
dividuals, it may also be possible for organizations to adopt
macrolevel policies that raise well-being for larger groups.
For instance, organizational psychologists strive to make
the workplace engaging and interesting. These benefits
might be worthwhile in themselves, or the increased hap-
piness that they provide may lead to increases in organi-
zational citizenship and productivity. Similarly, commu-
nity psychologists strive to enhance the quality of life
within neighborhoods and cities. Our findings that baseline
happiness can change, along with new studies showing that
interventions can raise levels of happiness, provide an
optimistic foundation for the various fields of applied
psychology.
Finally, if organizational policies can have an impact
on the happiness of large groups, it may be possible to
change the happiness of a society as a whole. Philosophers
such as J. S. Mill and Jeremy Bentham maintained that the
best society is one where the greatest numbers of citizens
experience the most happiness. Echoing this sentiment,
Diener and Seligman (2004) called for a system of national
accounts of well-being in which people’s happiness, mean-
ing, and engagement are assessed over time and in various
situations. The goal of such a program would be to help
policymakers understand when and why people are miser-
able and when and why they are happy. This information
would then allow policymakers to develop programs to
reduce misery and enhance happiness. Furthermore, it is
hoped that national accounts of well-being might lead to
policies that would heighten the engagement, joy, trust, and
affection of ordinary citizens who do not have extraordi-
nary problems. Fortunately, our findings indicate that the
goal of creating a happier society is not doomed by the
hedonic treadmill.
Although the research reviewed in this article provides
an optimistic picture of the possibility for change, the
processes of adaptation must still be carefully considered
when designing and assessing well-being interventions.
People might initially react positively to interventions just
as they do to naturally changing conditions, but over time
they may adapt to the intervention and return to their
former levels of well-being. Thus, effective interventions
must change people’s baseline well-being, and measure-
ments must be repeated over a long period of time to rule
out the possibility that the effectiveness of the intervention
is only temporary. A strong understanding of adaptation
theories will enable researchers to develop programs with a
great likelihood of long-term success.
Future Research and Conclusions
Although researchers have made progress in understanding
adaptation, several key issues remain. First, an overarching
question concerns the factors that lead to lasting change.
Why do adaptation effects appear to vary across different
events and circumstances? Although some theories (e.g.,
Kahneman & Thaler, in press) offer predictions about the
differential adaptation across varying events, these theories
do not seem to explain the full set of results. For instance,
it is unclear why people seem to exhibit a lasting effect of
unemployment on well-being even after they become re-
employed. A corollary question concerns how much con-
trol people have over adaptation: Can people slow adapta-
tion to good events and speed recovery from bad events?
Another important challenge is differentiating passive ac-
ceptance of negative circumstances versus active coping
and a positive resolution of events. Finally, our studies
raise the issue as to whether some components of well-
being adapt more readily than others. For instance, do
cognitive evaluations such as satisfaction adapt more
slowly than moods and emotions? These are exciting un-
answered questions about adaptation, questions that will
need to be answered before fully effective interventions can
be designed.
The treadmill model of happiness posited by Brick-
man and Campbell (1971) represents a milestone in psy-
chologists’ understanding of happiness, and our longitudi-
nal findings on marriage support the treadmill idea. Our
findings also indicate that different types of well-being may
change at different rates or even in different directions.
Furthermore, both experimental and longitudinal studies
now show that the strong form of the adaptation theory is
untenable. Adaptation may proceed slowly over a period of
years, and in some cases the process is never complete.
312 May–June 2006
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Finally, there are individual differences in the rates of
adaptation.
Those who provide interventions aimed at improving
subjective well-being need to understand the patterns in-
volved in adaptation so that successful interventions can be
designed. Although some of the studies we described in-
volve changes in life circumstances that are extreme, other
studies suggest that smaller interventions can make a dif-
ference. Adaptation is a powerful force, but it is not so
complete and automatic that it will defeat all efforts to
change well-being. The exciting research challenge is to
discover the factors that control the adaptation process.
Fortunately, research on coping, personality traits, and the
effectiveness of interventions all offer clues about factors
that influence adaptation. With the understanding that ad-
aptation may be incomplete and varies across persons, the
efforts to understand adaptation should be amplified.
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