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DUCIaI "EIWOTK ueuermlnants 0T UEPTBSSIOI'I JN Rosenquist'-"', JH Fowler3 and NA Christakis'-5 'Department of Psychiatry, Massachusetts
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The main outcome measure for the study is the Center for Epidemiological Studies Depression Scale (CES-D), which is a _________. ?

A.) Self-report measure of depression

D.) Clinical Diagnosis of Depression

C.) Rating of Depression by friends and family.

D.) Biological Measure of Depression

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DUCIaI "EIWOTK ueuermlnants 0T UEPTBSSIOI‘I JN Rosenquist‘-"’, JH Fowler3 and NA Christakis“-5 ‘Department of Psychiatry, Massachusetts General Hospital, Boston, MA, USA; 2Department of Health Care Policy, Harvard
Medical School, Boston, MA, USA; 3Department of Political Science, University of California, San Diego, CA, USA; “Department
of Health Care Policy, Harvard Medical School, Cambridge, MA, USA and 5Department of Sociology, Harvard University,
Cambridge, MA, USA The etiology of depression has long been thought to Include social environmental factors. To
quantitatively explore the novel possibility of person-to-person spread and network-level
determlnatlon of depresslve symptoms, analyses were performed on a densely interconnected
soclal network of 12067 people assessed repeatedly over 32 years as part of the Framingham
Heart Study. Longitudinal statistlcal models were used to examlne whether depresslve
symptoms In one person were assoclated with similar scores In friends, co-workers, siblings,
spouses and neighbors. Depressive symptoms were assessed using CES-D scores that were
available for subjects In three waves measured between 1983 and 2001. Results showed both
low and high CES-D scores (and classification as being depressed) In a given period were
strongly correlated with such scores In one‘s friends and neighbors. This association
extended up to three degrees of separation (to one’s frlends' frlends' friends). Female friends
appear to be especially Influential In the spread of depression from one person to another. The
results are robust to multiple network simulation and estimation methods, suggesting that
network phenomena appear relevant to the epidemiology of depression and would benefit
from further study. Molecular Psychiatry (2011) 16, 273—281; doi:10.1038/mp.2010.13; published online 16 March 2010 Keywords: depression; social networks; sociology; social norms; mood Introduction Depression is a significant cause of worldwide morbi-
dity and mortality. Current estimates suggest a life-
time incidence of between 13.3 and 17.1% in the
United States and a yearly cross-sectional preva-
lence ranging from 2.3—4.996.1 Using any number of
metrics, the cost of depression is enormous. For
example, disability, morbidity and mortality resulting
from depression was estimated to cost $86 billion in
the year 2000 alone.z The etiology of depression as an illness has been
conceptualized to have a number of interacting
biological, psychological and social components.3
This idea that social forces may impact mood symp-
toms was first hypothesized over 100 years ago in the
context of suicide by the sociologist Emile Durkheim.
He noted that suicide rates stayed the same across
time and across groups even though the individual
members of those groups came and went.‘ Durkheim’s
conclusion was that whether people took their own
lives depended in part on the kind of society they
inhabited. He noted that although depression and
suicide were seen as entirely individualistic. they
may be partly driven by social forces. More recent Correspondence: Dr ]N Rosenquist, Health Care Policy, Harvard
Medical School, 180 Longwood Avenue, Boston. MA 02115, USA.
E-mail: jrosenqufigmailmom Received 29 May 2009; revised 26 December 2009; accepted 27
December 2009; published online 16 March 2010 work on the social influences on depression find a
significant correlation between social factors such as
child abuse, disruptions in family functioning, stress-
ful life events and neighborhood characteristics?’3 The literature on social determinants of disease has
been augmented in recent years by a growing
literature focused on understanding the role of social
network structure on individual outcomes. Recent
work has yielded results suggesting that traits such as
obesity, smoking behavior. happiness and loneliness
may spread along social networks over time.EHS A
person’s structural position within a network, such as
their transitivity (whether their friends are friends
with each other] and centrality (whether they are
located in the middle or edge of the network) have
been found to affect the development of traits and
behaviors. For example, Bearman and Moody found
that social isolation and (among women) having
friends who were not friends with each other were
two factors predictive for suicidal ideation, suggest-
ing the structural components of a person's network
impacted their behavior.“5 In addition to such structural effects of network
position, there may also be influence effects, whereby
depression might spread among friends, family
members, co-workers and neighbors. While such
influence effects may have an intuitive appeal (most
people can no doubt think of instances where they
found themselves influenced by a family member
or friend), it is crucial to distinguish among three
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274 Swill netwuk determlmm d depression
JN Rnserlruisi at a! processes: [1] induction, whereby depression in one
person actually causes the depression of others;
[2] homophily, whereby depressed individuals
choose one another as friends and become connected
[that is, the tendency of like to attract like];" or
[3] confounding, whereby connected individuals
jointly experience contemporaneous exposures (such
as an economic downturn or co-residence in a poor
neighborhood”). To distinguish among these effects
requires repeated measures of depression,18 long-
itudinal information about network ties and [ideally]
information about the nature or direction of the ties
[for example, who nominated whom as a friend).
This paper tests the hypothesis that depressive
symptoms may spread from person to person to
person in social networks. Also tested is the hypo-
thesis that the structure of social networks may
influence, andJor may be influenced by, changes
in the CES-D scores of its members over time.
Finally, the analyses consider induction, homophily
and confounding as possible explanations for these
effects. A unique, longitudinal data set that contains
rich social network data as well as measures of
depressive symptoms is used for our analyses. Materials and methods Source data
Our study uses data obtained from participants in the
Framingham Heart Study [FHS]. The FHS is a
population-based, longitudinal, observational cohort
study that was initiated in 1948 to prospectively
investigate risk factors for cardiovascular disease.
Since then, it has come to be composed of four
separate but related cohort populations: [1] the
‘Original Cohort’ enrolled in 1948 (N: 5209); [2] the
‘Offspring Cohort’ (the children of the Original
Cohort and spouses of the children] enrolled in
1971 [N=5124]; [3] the ‘Omni Cohort’ enrolled in
1994 IN: 508, designed to increase ethnic diversity
of participants]; and [4] the ‘Generation 3 Cohort’
[the grandchildren of the Original Cohort} enrolled
beginning in 2092 (N=4095]. The Original Cohort
captured the majority of the adult residents of
Framingham in 1948 whereas the Offspring Cohort
included the great majority of the living offspring
of the Original Cohort in 1971, and their spouses.
Published reports describe these cohorts in more
detail?”1 Continuous surveillance and serial examinations of
these cohorts are the source of our longitudinal data.
Participant data includes physical exam, laboratory, battery testing [such as the Mini-Mental status exam],
questionnaire results and basic demographic informa-
tion. The Offspring study data is drawn from exams
completed roughly every 4 years over a 32-year period
[1971—2003], whereas the Original Cohort has data
available for approximately every 2 years over a 60-
year period. Within all cohorts, there is minimal
[ < 1%) loss to follow-up because of out-migration. For
the purposes of the analyses reported here, exam Molecular Psychiatry waves for the Original cohort were aligned with those
of the Offspring cohort. so that all subjects were
treated as having been examined at just seven waves
[in the same time windows as the Offspring, as
detailed in Supplementary Table 51]. The Offspring Cohort comprises the main source of
subjects as it is the source of ‘egos’ [the focal indi-
viduals in the network]. However, other FHS partici-
pants are included when listed as social contacts by
the egos (known as ‘alters’}. Therefore, whereas egos
come only from the Offspring Cohort, alters are drawn
from the entire set of FHS cohorts [including also the
Offspring Cohort itself]. This explains why the total
number of individuals in the FHS social network is
12 067. a number that includes individuals from
multiple cohorts [5124 from the offspring cohort,
3403 from the original cohort and 3540 from other
cohorts). Participant compliance with examinations is
excellent, with each wave having a participation rate
of about 80% [detailed in Supplementary Table S1}. To ascertain the network ties, a separate data set was
created that linked individuals through self-described
social ties. Specifically, information from archived,
handwritten documents that had been used by FHS
staff members to help keep track of individuals was
computerized. These sheets record the answers when
all 5124 of the egos were asked to comprehensively
identify friends, neighbors [based on address], co-
workers [based on place of employment] and relatives.
Although these tracking sheets were used as a way to
optimize participant follow-up, they also implicitly
contain valuable social network information. Another
unique feature of these administrative records that
makes them valuable for social network research relates
to the compact nature of the Framingham population in
the period from 1971 to 2007. This feature meant that
many of the nominated contacts were themselves also
participants of one or another FHS cohort, thus allowing for detailed data on them as well.
Through these self-described ties, we developed network links from FHS Offspring participants to other
participants in any of the four FHS cohorts. Thus, for
example, it is possible to know which participants have
a relationship [for example, spouse, sibling, friend, co-
worker, neighbor) with other participants. It is inter-
esting to note that each link between two people might
be identified by either party identifying the other; this
observation is most relevant to the ‘friend’ link, as we
can make this link either when A nominates B as a
friend, or when E nominates A (and, as discussed
below, this directionality is also methodologically
important}. People in any of the FHS cohorts may
marry or befriend or work with or live next to each
other. Figure 1 is an illustration of these network ties,
and shows the largest connected part of the network
(known as a ‘component’], of friends, spouses, and
siblings to illustrate the clustering of moderately
depressed (green nodes] and very depressed (blue
nodes] people in 2000. Finally, complete records of participants’ [and their
contacts’] addresses since 1971 were used in our
Screen Shot 2020-06-16 at 6.25.19 PM.png
analyses. Because of the high accuracy of addresses in
the FHS data (even though people spread out across
the USA over time], and the wealth of information
available about each subject's residential history, we
have been able to correctly assign addresses to
virtually all subjects. Through address mapping
technologies, it was possible to determine (1} who is
whose neighbor, and (2} what the geographical
distance between individuals was.22 Outcome measures Depression is measured using the Center for Epide-
miological Studies Depression Scale [CBS-D]. The
CBS-D is well established as a screening method for
depression with good reliability and validity.23‘2“ The
scale consists of a 20-item questionnaire where
subjects are asked how often during the previous Figure 1 Depression Clusters in the Framingham Social
Network. This graph shows the largest component of
friends, spouses and siblings at exam 7 [centered on the
year 2000]. There are 957 individuals shown. Each node
represents a subject and its shape denotes gender (circles
are male, squares are female). Lines between nodes indicate
relationship (red for siblings, black for friends and spouses].
Node color denotes the percentile score of the mean level of
depression in ego and all directly connected (distance 1}
alters, with yellow being below the 80th percentile, shades
of green being the 80th to 95th percentile, and blue being
above the 95th percentile [the most depressed]. Social netwrk mm of mm
.IN Rosanuist at at week they experienced a particular feeling that is
associated with depression, with four possible an-
swers, 0—1 days, 1—2 days, 3—4 days and 5—7 days.
Scoring yields a scale from 0 [least depressed] to 60
[most depressed], with a score of 16 or above used
to identify individuals with depressive illness. The
CES-D was administered between 1983 and 2001 at
times corresponding to the 5th, 6th, and 7th exami-
nations of the Offspring Cohort. The median year of
examination for these individuals was 1986 for exam
5, 1996 for exam 6 and 2000 for exam 7. Table 1 shows
summary statistics for the network, including mean
CES-D scores as well as social ties and demographic
information. The score means and incidence of
depression over time (CESD over >16) track with
other national estimates.‘ Analytic methods
To evaluate the association of an ego’s social network
with an ego’s depressive symptoms, various factors
were included in our models, ranging from the
prospective effect of alters’ symptoms, social network
variables and other control variables. Ego CIES-D
scores were regressed on ego age, gender, education
and depression in the previous exam, as well as alter
age, gender and depression in the current and
previous exam. Ego depression at the previous exam
was included to eliminate serial correlation in the
errors and also control ego’s genetic endowment and
any intrinsic, stable tendency to be depressed.
Including the alter's depression at the previous exam
helps control for homophily25 as shown by monte
carlo simulations in previous work.27 The key coefficient in the model that measures
the effect of induction is the variable for contem-
poraneous alter depression. Generalized estimating
equation [GEE] procedures were used to account
for multiple observations of the same ego across
waves and across ego-alter pairings.2a An indepen-
dent working correlation structure was assumed for
the clusters.“ These analyses underlie the results
presented in Figure 4. The GEE regression models
provide parameter estimates in the form of fl-coefli-
cients, whereas the results reported in the text and in
Figures 4 and 5 are in the form of risk ratios, which
are related to the exponential coefficients. Mean effect Table 1 Summary statistics for egos and alters [across all waves) Variable Mean ad. Min Max Observed cases
CBS-D BGDl'e 5.84 7.32 0 54: 7603
Depression status [CES-D score 16 +) 0.10 0.30 0 1 7603
Number of close friends 0.90 0.90 0 6 8309
Number of family members 2.81 3.0? 0 23 8309
Network centrality [times 1000] 0.87 12.90 0 235.35 0309I
Female 0.55 0.50 0 1 8309
Years of education 13.57 2.41 2 17 7159
Age 63.79 11.34 29.67 101.20 B305]I Abbreviation: CES-D, Center for Epidemiological Studies Depression Scale. 275 Molecular Psychiatry
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276 Social network deumlmm at depression
JN Rosemuist at at sizes and 95% confidence intervals are calculated by
simulating first difference in alter contemporaneous
depression status (changing from 0—1] using 100!)
randomly drawn sets of estimates from the coefiicient
covariance matrix and assuming all other variables
are held at their means.“ Results were checked using
a linear specification on the raw GEES-D score and
none of these models changed the significance of any
reported result. The models include exam fixed effects, which,
combined with age at baseline, account for the aging
of the population. The sample size is shown for each
model, reflecting the total number of all relevant ties,
with multiple observations for each tie if it was
observed in more than one exam, and allowing for
the possibility that a given person can have multiple
ties. Such multiple ties were handled with GE
procedures, clustering on ego. To test for the possibility of omitted variables or
contemporaneous events explaining the associations,
we used longitudinal models and also examined how
the type or direction of the social relationship
between ego and alter affects the association between
ego and alter. If unobserved factors drive the associa-
tion between ego and alter, then directionality of
friendship should not be relevant. Depression in the
ego and the alter will move up and down together in
response to the unobserved factors. In contrast, if an
ego names an alter as a friend but the alter does not
reciprocate, then we assume a causal relationship
would indicate that the alter would significantly
affect the ego, but the ego would not necessarily affect
the alter. The sensitivity of our results to model specification
was tested by conducting numerous other analyses
[not shown here] each of which had various strengths
and limitations, but none of which yielded substan-
tially different results than those presented. For
example, although only a single friend was identified
for most of the egos at any given time, the question of
how multiple observations on some egos [who had
more than one friend on one or more waves] affect the
s.e. of our models was considered. Huber—White
sandwich estimates with clustering on the egos
yielded very similar results. In another case, the
presence of serial correlation in the GEE models was
tested using a Lagrange multiplier test, which found
none after including the lagged dependent variable.31
To check for multicollinearity, we measured the
variance inflation factor for all variables in each
regression reported here. All variance inflation factor
values were 1.2 or lower, far below the value of 2.5
that typically warrants concern. The Kamada—Kawai algorithm was used to prepare
images of the networks, such as that in Figure 1.32 The
algorithm is a visualization tool that iteratively
repositions nodes to reduce the number of ties that
cross each other. The fundamental pattern of ties in a
social network [known as the ‘topology’] is fixed, but
how this pattern is visually rendered depends on the
analyst's objectives. Molecular Psychiatry To be sure any clustering of depressed people
shown in Figure 1 is not simply due to chance, the
following permutation test was implemented: the
observed network was compared with 1000 randomly
generated networks in which we preserved the
network topology and the overall prevalence of
depression but in which the assignment of the
depression value was randomly shuffled to each
node.“ For this test, depression was dichotomized
to be 1 if the respondent had a CES-D score of 16 or
greater, and 0 otherwise. If clustering in the social
network is occurring, then the probability that an alter
is depressed given that an ego is depressed should be
higher in the observed network than in the random
networks. This procedure also allows us to generate
confidence intervals and measure how far, in terms of
social distance, the correlation in depression between
ego and alter reaches. Results Figure 1 shows the largest connected component of
friends, spouses and siblings and illustrates the
clustering of moderately depressed (green nodes}
and very depressed [blue nodes] people. In addition
to illustrating clustering, this graph also visually
suggests a relationship between depressive symptoms
and being socially peripheral (being located on the
edge of the network]. Figure 2 shows the correlation of alters depression
scores over time based on their degrees of separation
from an ego. The results suggest that there is a
significant relationship between ego and alter depres-
sion, and this relationship extends up to three degrees
of separation. In other words, a person’s depression
depends not just on his friend’s depression, but also
extends to his friend’s friend and his friend’s friend’s
friend. The full network shows that subjects are 93%
(95% CI 59—135%) more likely to be depressed if a
person they are directly connected to (at one degree of
separation] is depressed. The size of the effect for
people at two degrees of separation (the friend of a
friend) is 43% (95% CI 21—70%} and for people at
three degrees of separation [the friend of a friend of a
friend} is 37% (95% CI 16—60%]. At four degrees of
separation the effect disappears [—2%, 95% CI —15—
11%)., a result that is in line with other results that
have shown similar drop-offs after three degrees of
separation, including obesity, smoking, happiness
and loneliness."—12 To evaluate the impact of one aspect of network
structure, our analyses, shown in Table 2, suggest that
people with more friends and social connections are
less likely to experience depressive symptoms in the
future [Model 1], in keeping with past work. Each
extra connection reduces the CES-D score by about
0.3 points. Interestingly, the same model shows that
the number of family members has no effect at all
(P: 0.32}. The results in Model 2 suggest that people
who feel depressed are likely to have significantly
fewer friends in the future. In fact, compared with
Screen Shot 2020-06-16 at 6.25.48 PM.png
Social network ileum-hm of depression w
ill Rasmquist at al people who show no depressive symptoms, they will 27?
lose about 6% of their friends on average over a
roughly 4-year period. For comparison, Model 3
shows that depression has no effect on the future
number of family members a person has. These
results are symmetric to both incoming and outgoing
ties [not shown—available on request); that is. depres-
sed people tend to receive fewer friendship nomi-
nations, but they also tend to name fewer people as
friends as well. These results suggest that a person’s
depression may shape their social network as well as
be shaped by it (further evidence of this effect is
included in the online appendix]. In Table 3, we show how depression is influenced
by an additional measure called ‘eigenvector central-
ity’ which indicates how central a person is in the
whole network (see appendix for formal definition].
The larger this value, the better connected a person is
to all people in the network either directly via friends § '8‘ Relative Increase (96) in Probability
8 Ego Is Depressed Given Alter ls Depressed
8 all 1 2 3 4 O Alter Social Distance Figure 2 Social Distance and Depression in the Framing-
ham Social Network. This figure shows for each exam the
percentage increase in the likelihood a given ego is depressed
if a friend or family member at a certain social distance is
depressed (where depressed is defined as a score greater than
16 or greater on the CBS-D). Values are derived by comparing
the conditional probability of being depressed in the
observed network with an identical network [with topology
and incidence of depression preserved] in which the same
number of depressed subjects are randomly distributed. Alter
social distance refers to closest social distance between the
alter and ego [alter = distance 1, alter’s alter =distance 2, etc.].
Error bars show 95% confidence intervals. CES-D, Center for
Epidemiological Studies Depression Scale. and family or indirectly via the friends and family of
their friends and family. The model shows that
network centrality in the previous exam significantly
decreases the likelihood of depression, and it does so
even when we control for the number of direct ties to
friends and family. This suggests that a person’s
relationship to the whole network is important, above
and beyond how well connected a person is to
immediate friends and family. Figure 3 shows the smoothed bivariate relationship
between the fraction of a person’s friends and family
who are depressed at one exam, and the likelihood
they will be depressed at the following exam. Here,
the issue is not how many contacts a person has or how central a person is, but whether a large or small Table 2 Prospective influence of friends and family on depression and vice verse Dependent variable
Currant CES—D score Current number of friends CLu’rent number offomfly
Car-6.5“}c s.e. P-voiue Co-eff s.e. P-vniue Co-eff s.e. P-value
Previous CES-D score 0.456 0.019 0.000 —0.002 0.001 0.003 —0.001 0.001 0.142
Previous number of friends 70.289 0.093 0.002 0.901 0.007 0.000 0.033 0.003 0.000 Previous number of family 0.024 0.025 0.323 —0.003 0.002 0.042 —0.029 0.007 0.000
Age 0.022 0.008 0.007 —0.002 0.000 0.000 0.001 0.001 0.004
Years of education 70.169 0.037 0.000 0.002 0.002 0.206 70.006 0.003 0.020
Female 1.106 0.159 0.000 —0.015 0.009 0.091 0.015 0.012 0.213
Exam 7 1.159 0.169 0.000 0.005 0.009 0.543 0.039 0.012 0.001
Constant 74.373 1.450 0.003 0.113 0.076 0.135 70.250 0.093 0.007
Deviance 244229 723 1291
Null deviance 327763 4893 57482
N 6113 6113 6113 Abbreviation: CES-D, Center for Epidemiological Studies Depression Scale.
Results for linear regression of ego’s CES-D score, number of friends, and number of family members at current exam on previous CES-D score, number of friends, and number of family plus other covariates. Models were estimated using a general
estimating equation (GEE) with clustering on the ego and an independent working covariance structure. Models with an
exchangeable correlation structure yielded poorer fit. Fit statistics show the sum of squared deviance between predicted and
observed values for the model and a null model with no covariates. Molecular Psychiatry
Screen Shot 2020-06-16 at 6.26.24 PM.png
273 Social network drurmlmnl: of depression
JN Rosemulsi er al Tabla 3 Prospective influence of centrality on depression Dependent variable:
current CES-D score Ctr-eff s.e. P-vrrl'ue —8.285 4.142 0.045
—0.278 0.094 0.0 03 Previous network centrality
Previous number of friends Previous number of family 0.456 0.019 0.000
Previous CES-D score 0.036 0.028 0.195
Age 0.022 0.003 0.005
Years of education —0.163 0.03? 0.000
Female 1.110 0.159 0.000
Exam 7 1.101 0.109 0.000
Constant —4.469 1.454 0.002
Deviance 244061 Null deviance 327588 N 6113 Abbreviation: CES—D. Center for Epidemiological Studies
Depression Scale. Model of ego‘s CES-D score at current exam regressed on
measures from the previous exam including ego’s network
centrality, number of friends, number of family, plus other
covariates. The model was estimated using a general estimating
equation (GEE) with clustering on the ego and an independ-t
working covariance structure. Models with an exchangeable
correlation structure yielded poorer tit. Fit siaiisiics show sum
of squared deviance between predicted and observed value:
for the model and a null model with no covariates. The main
results [coefficients in bold] show that network cenirality is
associated with a decrease in future depressive symptoms,
even controlling for the number of friends and family. This suggests that connection to more socially distant alters [for
example, friends of friends] also influences depression. Probability Ego Will Be Depressed
(CES—D 16+) at Next Exam
I P o o
| | | | i | |
0 20 40 60 80 100 Alters Who Feel Depressed {as} Figure 3 Depressed Alters in the Framirlgham Social Net- work. This plot shows that the probability of being depressed
[CES—D score of 16 or greater] in exams 6 and 7 is positively associated with the fraction of their friends and family in the
previous exam who are depressed. Blue line shows smoothed
relationship based on hivariate DOESS regression, and dotted lines indicate 95% confidence intervals. CES-D, Center for
Epidemiological Studies Depression Scale. Molecular Psychiatry Table 4 Influence of number of depressed alters on ego
depression Dependent variable: CBS-D score Ctr-eff sue. P-Vrrl'rre
Previous number of 0.762 0.190 0.000
depressed alters
Previous number of —0.128 0.058 0.026
non-depressed alters
Previous CES-D score 0.431 0.021 0.000
Age —0.011 0.010 0.265
Years of education —0.136 0.041 0.001
Female 1.129 0.172 0.000
Exam :7 1.45? 0.191 0.000
Constant 74.925 1.611 0.002
Deviance 190439
Null deviance 251500
N 4913 Abbreviation: CES-D, Center for Epidemiological Studies
Depression Scale. Results for linear regression of ego’s depression on previous
depression, number of depressed friends and family [16 or
greater on CBS-D], number of non-depressed friends and
family, and other covariates. Models were estimated using a
general estimating equation [GEE] with clustering on the
ego and an independent working covariance structure
Models with an exchangeable correlation structure yielded
poorer fit. Fit statistics show sum of squared deviance
between predicted and observed values for the model and a
null model with no covariates. fraction of these contacts is also depressed. The
relationship is significant and nearly doubles the
likelihood of depression for the average person who
is surrounded by other depressed people compared
with those who are not connected to anyone who is
depressed. Analyses testing the impact of depressed alters
over time are presented in Table 4. The results show
that each additional depressed alter significantly
increases the number of days a subject feels depres-
sed [P<0.001]. Conversely, each additional non-
depresssd alter significantly decreases the number
of days a subject feels depressed (P=0.026]. But these
effects are asymmetric: depressed alters are about
six times more influential than non-depressed alters,
and the difference in these effect sizes is itself signi-
ficant (P: 0.0006]. Therefore, the feeling of depres-
sion seems to spread more easily than its absence. Results of GE models that estimate specific eflects
for friends, spouses, co-workers, siblings and neigh-
bors are presented in Figure 4. If a friend is depressed,
this increases the probability ego and is depressed by
110% (95% CI 6—290%]. Among friends, it is possible
to distinguish additional possibilities. As each person
was asked to name a friend, and not all of these
nominations were reciprocated, we have ego-per-
ceived friends [denoted 'friends’], ‘alter-perceived
friends’ [alter named ago as a friend, but not vice
Screen Shot 2020-06-16 at 6.26.39 PM.png
versa] and ‘mutual friends’ [ego and alter nominated
each other]. If mutual friends are depressed, it
increases the likelihood of depression for the ego by
359% [95% CI: 25—1095%]. In contrast, the influence Alter Type Fnend Mutual Friend
Alter-Perceived Friend
Male Friend Female Friend
Spouse Sibling Next-Door Neighbor
Same-Block Neighbor
coworker I I I I I I
O 200 400 600 800 1000
Increase in Risk of Ego Depression (96)
If Alter Becomes Depressed Figure 4 Alter Type and Depression in the Framingham
Social Network. This graph shows the change in likelihood
of depression given that an alter is depressed. Estimates are
based on generalized estimating equation legit models of
depression on several different sub-samples of the Framing-
ham Heart Study Social Network. The dependent variable
in each model is ego depression status and independent
variables include lagged ego depression status. alter
depression status, lagged alter depression status, ego age,
gender, and education and fixed effects for each wave. Full
models and equations are available in the appendix. Mean
effect sizes and 95% confidence intervals were calculated
by simulating first difference in alter contemporaneous
depression status (changing from 0—1) using 1000 randomly
drawn sets of estimates from coefficient covariance matrix
and assuming all other variables are held at their means. Table 5 Association of friend's depression and age depression of alter-perceived friends is not significant [P=0.38].
These results suggest that the associations in the
social network were not merely because of confound-
ing, for, in the null hypothesis, one would assume
that the significance and effect sizes for different
types of friendships should be the same. For example,
if some third factor were explaining both ego and alter
depression, there should be no observed influences
from directionality or strength of the social lie in
question. Further analyses of person-to-person effects
can be found in the online appendix. In particular, we
show that the main results remain significant even
when we control for dynamic changes in the number
of network ties to each person, longitudinal attrition,
occupational prestige and marital status. These results
can also be found in the Supplementary online appendix An intriguing diflerence between inter-personal
effects in depression and previous work with respect
to happiness11 is shown in gender effects. When
friends are divided up by gender in Table 4, depres-
sion is found to spread much more easily from
women than from men. When a female friend
becomes depressed, it increases the probability that
the ego is depressed by 142% [CI 18—33196]. In
contrast, when a male friend becomes depressed, on
average it has no significant effect (P: 0.34]. However,
similar differences in receptivity were not found;
men and women appear to be equally sensitive to their friends [Table 5]. Discussion These results support the hypothesis that depressive
symptoms as defined by CES-D scores can be observed to travel along social networks. They suggest that both
decreases and increases in CES-D scores [and classifi- Alter type
Friend Mutual friend Alterhpemeivedfiiend Male Friend Female friend
Alter currently depressed 0. 70 [0.36] 1. 43 [0.61] 0.49 [0.56] —0.92 [0.96] 0.93 [0.33]
Alter previously depressed 0. 68 [0. 42] 2. 23 [0.63] 0.71 [0.45] 0.43 [0.75] 0.77 [0.44]
Ego previously depressed 2. 34 [0. 31] 2. 35 [0. 72] 1.12 [0.53] 2.57 [0.71] 2.25 [0.33]
Exam 7 0. 47 [0. 27] 70. 75 [0.64] 0.22 [0.43] 70.20 [0.50] 0.03 [0.32]
Ego’s age 0. 00 [0. 02] 0. 03 [0. 04] 0.01 [0.02] 0.03 [0.04] —0.02 [0.03]
Ego female 0.63 [0. 40] —0. 35 [0. as] 1.09 [0.45] 1.42 [0.60] 0.30 [0.70]
Ego’s years of education —0. 24 [0. 09] —0. 42 [0.21] 0.03 [0.10] —0.25 [0.13] —0.25 [0.12]
Constant 70. 4s [2. 13] 73. 24 [4. 25] 74.39 [2.41] 72.43 [3.51] 0.79 [2.65]
Deviance 51 11 36 12 38
Null deviance 66 18 38 16 49
N 853 265 572 359 499 Coefficients and standard errors in parenthesis for linear logit regression of ego’s depression status on covariates are shown.
Observations for each model are restricted by type of relationship [for example, the leftmost model includes only
observations in which the ego named the alter as a ‘fliend’ in the previous and current period]. Models were estimated using
a general estimating equation with clustering on the ego and an independent working covariance structure. Models with an
exchangeable correlation structure yielded poorer fit. Fit statistics show sum of squared deviance between predicted and
observed values for the model and a null model with no covariates. 279 Molecular Psychiatry
Screen Shot 2020-06-16 at 6.26.52 PM.png
280 Social network deurrnlmm at depression
JN Rnsenquin er ai cation as being depressed] were strongly correlated
with depression measures in one’s friends and neigh-
bors. The correlations decrease significantly the further
away (in terms of degree of separation] an alter is in an
ego’s social network. This is, to our knowledge, the
first such analysis performed looking specifically at
depressive symptoms in such a network-based, long-
itudinal manner. These results are similar to previous
work showing the spread of obesity, smoking and
happiness within social networks.‘HI Another important finding related to the how CES-D
scores and depression appeared to affect (and be
affected by] the actual architecture of the network
itself. The results su'est that not only may depressed
mood spread across social ties, but also that depression
depends on how connected individuals are and where
they are located within social networks. Our work
suggests that to understand someone's HES-D score,
one must ask both where they are situated within a
network (for example, how central they are to the
network or how many friends they have], and how the
people around them are actually feeling (quite apart
from their topological location]. An alternative inter-
pretation of these results is that causality may be
reversed, meaning that the onset of depression affects
social networks themselves by inducing tie formation
andjor dissolution; however, analyses of our data
indicates that CES-D scores did not predict changes
in ties, thus making this hypothesis less likely?1 A related topological finding comes from the
analysis of individuals on the periphery of the net-
work. These people have significantly worse CES-D
scores and have fewer friends. Their isolation appears
to be correlated not only with having fewer friends as
baseline, but also the likelihood for them to cut any
remaining ties that they have left. Given that these
peripheral individuals’ depression is correlated with
future scores of those friends further within the
network, it suggests that isolation as well as clustering
may have an impact on the spread of depressive
symptoms. This finding also suggests that selective
targeting of more socially isolated individuals for
interventions might be particularly cost effective from
a societal standpoint, benefitting both them and others. There are some surprising findings with regards to
types of alters and the observed effects. The gender of
alters appears to be significant, with women appear-
ing more influential than men over time. While recent
work has challenged the idea that women are more
‘emotional’ than men, there remains a vast literature
on the differences in emotional expression between
men and women.“36 For example, women have been
found to be more emotionally expressive than men,
often using non-verbal cues to express their emotional
state.37‘39 One conceivable hypothesis is that, based
on these differences, women may be more effective
at communicating certain mood states within dyads,
a trait that may have an evolutionary origin.“ The results also would seem to suggest that spouses
are significantly less influential than friends over the
course of time. This finding, also found in previous Molecular Psychiatry work on happiness,“ on the surface appears puzzling
(and conceivably problematic). One would imagine
that spouses would be particularly influential on
each other. For example, work in cross-sectional
data suggests a strong correlation between spouses
with regards to mood symptoms.“42 However, further
work by Siegel et a1.“ showed using that, when
looking at longitudinal data on spousal mood, and the
across-time correlation of spousal changes in mood
symptoms, the magnitude of effects found were quite
similar to those found in this paper. One possible
explanation for these findings is that there is more
homophily between couples than friends. Put another
way, just as spouses are sometimes referred to as
‘joined at the hip,’ so might be their CES-D scores
from one period to the next. Our models, which
control for homophily on depression (that is, the
tendency of spouses to choose each other based on a
predilection to a certain mood}, can thus uncover a
possibly greater residual effect of induction between
friends than between spouses. This finding would
suggest that, while heterophily ['opposites attract’}
may be an important factor in mate selection for some
traits, it might not be with regards to factors that
influence CES-D scores." This work has a few notable limitations. It does not
randomize individuals into social networks, thus
leaving open the possibility that these results may
in part reflect homophily-driven selection bias on the
basis of unobserved phenotypes that influence the
development and transmission of depressive symp-
toms over time. Our group is actively addressing
this question through the use of quasi-experimental
approaches and other methods in ongoing work.
Another limitation is that the outcome measure
(CES-D] is not a clinical tool, so it is not possible to
make any specific conclusions about the spread of
clinical depression in our sample. Also, the sample is
somewhat homogenous and does not have a signifi-
cant percentage of underrepresented minorities in it.
Furthermore, our data set captures a limited number
of close friendship ties, thus we cannot extend our
analyses to more broad social network ties [such as
online interactions). Finally, the His social network
data set is unusual due to its longitudinal nature and
relative completeness; it is our hope that the further
collection of social network data in other settings
will provide more opportunities to evaluate such
hypotheses. In conclusion, we consider these results to be an
important step towards better understanding the
impact of interpersonal relationships and social net-
works on the development of depressive symptoms.
By identifying how the structure of networks may
determine the spread of clinically relevant conditions
(and vice versa], future policy may be able to target
individuals within a network to maximize the impact
of a policy. An example of this, known as ‘seeding,’
seeks to use well-connected individuals to spread
information and is the subject of a number of ongoing
research projects.“ We hope that social networks and
Screen Shot 2020-06-16 at 6.27.08 PM.png
Social network determinants of depression
UN Rosenquist et al
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Supplementary Information accompanies the paper on the Molecular Psychiatry website (http://
Molecular Psychiatry

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