732 vII. APPLICATIONS  AND  IMPLICATIONS
ies that examine the heritability of the vari -
ous SWB components. In the typical design, 
identical and fraternal twins complete hap -
piness measures and the cross-twin correla -
tions are compared. Simple additive genetic 
effects are implied when the cross-twin cor -
relation for identical twins is approximately 
twice as large as the cross-twin correlation 
for fraternal twins. Nonadditive genetic ef -
fects are implied when the ratio of identical 
to fraternal twin correlations is higher than 
two (though more sophisticated designs are 
often required to isolate these effects). Ex -
tensions of the basic twin design can be used 
to examine additional questions about the 
heritability of happiness. For instance, the 
inclusion of twins raised in different house -
holds allows researchers to isolate shared- 
environment effects more precisely and 
to rule out alternative explanations of the 
results. In addition, by acquiring multiple 
waves of data over time, researchers can 
examine the genetic effects on stability and 
change.
A number of studies have been conducted 
to examine the heritability of various well-
being measures, and most arrive at similar 
conclusions about the broad heritability of 
SWB (for a review see Roysamb, Nes, & 
Vitterso, 2014). For instance, in perhaps 
the first such study, Tellegen and colleagues 
(1988) examined twins reared together and 
those reared apart to estimate the contribu -
tion of genes and environment to various 
scales from the Multidimensional Personal -
ity Questionnaire. The estimated heritabili -
ties of the well-being facet and global posi -
tive emotionality factor were .48 and .40, 
respectively. The heritabilities of the stress 
reaction facet and negative emotionality 
factor were .53 and .55, respectively. These 
estimates suggest that about half of the vari -
ance in these well-being measures could be 
accounted for by shared genes. Importantly, 
this study also suggested that growing up in 
the same household played a very small role 
in the similarity of twins. The only signifi -
cant shared-  environment effect was for the 
global positive emotionality trait, where this 
component accounted for 22% of the vari -
ance.
One criticism that could be raised about 
this study is that the assessed measures were 
not developed as measures of SWB. Instead, they were developed to assess stable person -
ality characteristics that have an affective 
core. Thus, they may not reflect “happiness” 
as it is typically studied by SWB researchers. 
However, studies have replicated this basic 
effect using a variety of measures. For in -
stance, Roysamb, Harris, Magnus, Vitterso, 
and Tambs (2002; also see Roysamb, Tambs, 
Reichborn-  Kjennerud, Neale, & Harris, 
2003) examined the heritability of a four-
item global well-being measure that assessed 
satisfaction, happiness, nervousness, and 
activity level. Like Tellegen and colleagues 
(1988), they found that about 50% of the 
variance could be accounted for by a genetic 
component, and the shared-  environment 
component contributed very little. Similarly, 
Stubbe, Posthuma, Boomsma, and De Geus 
(2005) reported that 38% of the variability 
in the Satisfaction with Life Scale (SWLS; 
Diener, Emmons, Larsen, & Griffin, 1985) 
was heritable.
These studies consistently show that re -
gardless of the measure used, broad heri -
tability estimates for well-being constructs 
tend to fall between .40 and .50. However, 
this does not mean that behavioral genet -
ics research is without controversy. Perhaps 
the most controversial issue relates to ques -
tions regarding the heritability of the stable 
component of happiness. According to one 
prominent model of SWB, people have a set-
point level of happiness that is stable over 
time (Brickman & Campbell, 1971). Events 
and life circumstances can move people 
away from this set point, but eventually 
people adapt and return to baseline. Thus, 
at any given moment, a person’s happiness 
score might reflect the combined effects of 
the stable baseline and the temporary influ -
ence of life events. If so, the heritability of 
happiness might be higher if the stable base -
line could be isolated from these temporary 
deviations.
In 1996, Lykken and Tellegen attempted 
to accomplish this goal using data from 
identical and fraternal twins who com -
pleted happiness measures on two occa -
sions separated by approximately 10 years. 
They found that the stability of well-being 
was about .50, which means that approxi -
mately 50% of the variance on either of the 
two occasions was stable trait variance. But 
more importantly, they found that the cross-