Nicholas Christakis

Nicholas Christakis
Yale University | YU · Department of Statistics

About

319
Publications
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Publications

Publications (319)
Article
Full-text available
Targeting structurally influential individuals within social networks can enhance adoption of health interventions within populations. We tested the effectiveness of two algorithms to improve social contagion that do not require knowledge of the whole network structure. We mapped the social interactions of 2,491 women in 50 residential buildings (c...
Article
Full-text available
Objective. When medical resources are scarce, clinicians must make difficult triage decisions. When these decisions affect public trust and morale, as was the case during the COVID-19 pandemic, experts will benefit from knowing which triage metrics have citizen support. Design. We conducted an online survey in 20 countries, comparing support for 5...
Article
Trellis is a mobile platform created by the Human Nature Lab at the Yale Institute for Network Science to collect high-quality, location-aware, off-line/online, multi-lingual, multi-relational social network and behavior data in hard-to-reach communities. Respondents use Trellis to identify their social contacts by name and photograph, a procedure...
Preprint
Full-text available
Although vaccines are crucial for giving pandemic-stricken societies the confidence to return to socioeconomic normalcy, vaccination may also induce laxity in personal protective behaviours (e.g., handwashing, facemask use). We use the quasi-experimental context of the COVID-19 vaccine rollout across the United States to quantify the impact of diff...
Chapter
Machines powered by artificial intelligence increasingly mediate our social, cultural, economic, and political interactions. This chapter frames and surveys the emerging interdisciplinary field of machine behaviour: the scientific study of behaviour exhibited by intelligent machines. It outlines the key research themes, questions, and landmark rese...
Article
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Household food insecurity (HFI) is a significant problem in the developing world. Relationships between HFI and nutrition, physical growth, and development have been elucidated; less is known about the non-nutritional impacts among individuals living in rural areas in low-income countries. The aim of this study was to determine if HFI is a risk fac...
Article
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Kinship networks are a fundamental social unit in human societies, and like social networks in general, provide social support in times of need. Here, we investigate the impact of sudden environmental shock, the M s 7.0 2013 Ya’an earthquake, on the mobile communications patterns of local families, which we operationalize using anonymized individua...
Article
Full-text available
Trellis is a mobile platform created by the Human Nature Lab at the Yale Institute for Network Science to collect high-quality, location-aware, off-line/online, multi-lingual, multi-relational social network and behavior data in hard-to-reach communities. Respondents use Trellis to identify their social contacts by name and photograph, a procedure...
Preprint
We examined the impact of voting on the spread of COVID-19 after the US primary elections held from March 17 to July 11, 2020 (1574 counties across 34 states). We estimated the average effect of treatment on the treated (ATT) using a non-parametric, generalized difference-in-difference estimator with a matching procedure for panel data. Separately,...
Article
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Cooperation in human groups is challenging, and various mechanisms are required to sustain it, though it nevertheless usually decays over time. Here, we perform theoretically informed experiments involving networks of humans (1,024 subjects in 64 networks) playing a public-goods game to which we sometimes added autonomous agents (bots) programmed t...
Article
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Sudden, large-scale, and diffuse human migration can amplify localized outbreaks into widespread epidemics.1–4 Rapid and accurate tracking of aggregate population flows may therefore be epidemiologically informative. Here, we use mobile-phone-data-based counts of 11,478,484 people egressing or transiting through the prefecture of Wuhan between 1 Ja...
Article
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Friendship and antipathy exist in concert with one another in real social networks. Despite the role they play in social interactions, antagonistic ties are poorly understood and infrequently measured. One important theory of negative ties that has received relatively little empirical evaluation is balance theory, the codification of the adage “the...
Article
Full-text available
Background: Men who have sex with men (MSM) globally have a high burden of curable sexually transmitted infections (STIs). MSM do not frequently receive rectal STI testing because of several barriers, such as not being out (disclosure of sexual behavior). We evaluate whether Chinese MSM select an STI test (rectal vs urethral) appropriate for their...
Article
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In emergencies, social coordination is especially challenging. People connected with each other may respond better or worse to an uncertain danger than isolated individuals. We performed experiments involving a novel scenario simulating an unpredictable situation faced by a group in which 2480 subjects in 108 groups had to both communicate informat...
Article
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Clinical evidence suggests that mindfulness meditation reduces anxiety, depression, and stress, and improves emotion regulation due to modulation of activity in neural substrates linked to the regulation of emotions and social preferences. However, less was known about whether mindfulness meditation might alter pro-social behavior. Here we examined...
Article
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We recommend the immediate universal adoption of cloth facemasks, including homemade, and accompanying policies to increase the supply of medical masks for health workers. Universal adoption will likely slow the spread of the COVID-19 virus by reducing transmission from asymptomatic individuals. We provide strongly suggestive evidence from cross-co...
Article
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Background WHO recommends that men who have sex with men (MSM) receive gonorrhoea and chlamydia testing, but many evidence-based preventive services are unaffordable. The pay-it-forward strategy offers an individual a gift (eg, a test for sexually transmitted diseases) and then asks whether they would like to give a gift (eg, a future test) to anot...
Article
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Background: Adolescent pregnancy and childbirth are common throughout Central America. While gendered beliefs promoting motherhood are a known risk factor, their association with adolescent childbirth within the social networks of Central American communities is unknown. Methods: This was a cross-sectional study looking at adolescent childbirth...
Preprint
Full-text available
Sudden, large-scale, and diffuse human migration can amplify localized outbreaks into pandemics. Rapid and accurate tracking of human population mobility using reliable mobile phone data could therefore be helpful for policy responses. Here, we examine mobile phone geolocation data for all 18,514,920 counts of individuals egressing or transiting th...
Article
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Social robots are becoming increasingly influential in shaping the behavior of humans with whom they interact. Here, we examine how the actions of a social robot can influence human-to-human communication, and not just robot–human communication, using groups of three humans and one robot playing 30 rounds of a collaborative game ( n = 51 groups). W...
Preprint
Full-text available
Background. To evaluate whether Chinese men who have sex with men (MSM) select an STI test (rectal vs urethral) appropriate for their sexual behavior (insertive and/or receptive role in anal sex). Methods. We studied uptake of gonorrhea and chlamydia testing among Chinese MSM (N=431) in a multi-site RCT (December 2018 to January 2019). We collected...
Preprint
Full-text available
Background. To evaluate whether Chinese men who have sex with men (MSM) selectan STI test (rectal vs urethral) appropriate for their sexual behavior (insertive and/orreceptive).Methods. We studied uptake of gonorrhea and chlamydia testing among ChineseMSM (N=431) in a multi-site randomized controlled trial (RCT) (December 2018 toJanuary 2019). We c...
Chapter
We develop and analyze a tractable empirical model for strategic network formation that can be estimated with data from a single network at a single point in time. We model the network formation as a sequential process where in each period a single randomly selected pair of agents has the opportunity to form a link. Conditional on such an opportuni...
Preprint
We introduce CurmElo, a forced-choice approach to producing a preference ranking of an arbitrary set of objects that combines the Elo algorithm with novel techniques for detecting and correcting for (1) preference heterogeneity induced polarization in preferences among raters, and (2) intransitivity in preference rankings. We detail the application...
Article
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Resource sharing can impose an economic trade-off: One person acquiring resources may mean that another cannot. However, if individuals value the social process itself that is a feature of economic exchanges, socio-structural manipulations might improve collective welfare. Using a series of online experiments with 600 subjects arrayed into 40 group...
Article
Genetic correlation between mates at specific loci can greatly alter the evolutionary trajectory of a species. Genetic assortative mating has been documented in humans, but its existence beyond population stratification (shared ancestry) has been a matter of controversy. Here, we develop a method to measure assortative mating across the genome at 1...
Conference Paper
Full-text available
Background Gonorrhea and chlamydia testing is poor among Chinese MSM with HIV risk. Furthermore, gonorrhea and chlamydia testing programs are poorly funded and unlinked to HIV testing services. Pay-it-forward offers an individual a gift (e.g. an STD test) and then asks whether they would like to give a gift to another person. This study assesses th...
Article
Full-text available
Background: Mosquito net use is an essential part of malaria prevention. Although previous research has shown that many people sleep under a mosquito net in endemic areas, it is unknown whether people underestimate how common it is to sleep under a net every night. Furthermore, perceived social norms about whether most others sleep under a mosquit...
Article
Rationale: HIV-related stigma profoundly affects the physical and social wellbeing of people living with HIV, as well as the community's engagement with testing, treatment, and prevention. Based on theories of stigma elaborating how it arises from the relationships between the stigmatized and the stigmatizer as well as within the general community...
Article
Background: Perioperative magnetic resonance imaging (MRI) is frequently used in breast cancer despite unproven benefits. It is unclear whether surgeons' use of breast MRI is associated with the practices of other surgeons to whom they are connected through shared patients. Methods: We conducted a retrospective study using Medicare data to ident...
Article
Full-text available
Machines powered by artificial intelligence increasingly mediate our social, cultural, economic and political interactions. Understanding the behaviour of artificial intelligence systems is essential to our ability to control their actions, reap their benefits and minimize their harms. Here we argue that this necessitates a broad scientific researc...
Article
Full-text available
Technologically enabled sharing-economy networks are changing the way humans trade and collaborate. Here, using a novel ‘Wi-Fi sharing’ game, we explored determinants of human sharing strategy. Subjects (N = 1,950) participated in a networked game in which they could choose how to allocate a limited, but personally not usable, resource (representin...
Article
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Adolescent childbearing rates are higher in Central America than almost anywhere else on the planet. However, in this research we discovered that adolescent childbearing exhibits variability from one village to another, offering the possibility that we might discover factors associated with this spatial variability that can help us understand key f...
Article
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Negative (antagonistic) connections have been of longstanding theoretical importance for social structure. In a population of 24,696 adults interacting face to face within 176 isolated villages in western Honduras, we measured all connections that were present, amounting to 105,175 positive and 16,448 negative ties. Here, we show that negative and...
Article
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Background Perioperative MRI has disseminated into breast cancer practice despite equivocal evidence. We used a novel social network approach to assess the relationship between the characteristics of surgeons’ patient‐sharing networks and subsequent use of MRI. Methods We identified a cohort of female patients with stage 0‐III breast cancer from t...
Article
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From decentralized banking systems to digital community currencies, the way humans perceive and use money is changing1–3, thus creating novel opportunities for solving important economic and social problems. Here, we study Sardex, a fast-growing community currency in Sardinia (involving 1,477 businesses arrayed in a network with 48,170 transactions...
Preprint
Full-text available
Friendship and antipathy exist in concert with one another in real social networks. Despite the role they play in social interactions, antagonistic ties are poorly understood and infrequently measured. One important theory of negative ties that has received relatively little empirical evaluation is balance theory, the codification of the adage `the...
Article
Sociologists, economists, epidemiologists, and others recognize the importance of social networks in the diffusion of ideas and behaviors through human societies. To measure the flow of information on real‐world networks, researchers often conduct comprehensive sociometric mapping of social links between individuals and then follow the spread of an...
Article
Full-text available
HIV testing is an essential part of treatment and prevention. Using population-based data from 1664 adults across eight villages in rural Uganda, we assessed individuals’ perception of the norm for HIV testing uptake in their village and compared it to the actual uptake norm. In addition, we examined how perception of the norm was associated with p...
Article
Full-text available
We investigated the household-level social network correlates of acceptance of intimate partner violence (IPV) in rural, agrarian settings of Honduras and Uganda, two low-income countries with unequal access to resources based upon gender. We collected complete social network data in each location (Honduras in 2014 and Uganda in 2012), across a div...
Article
Importance Physicians are embedded in informal networks in which they share patients, information, and behaviors. Objective We examined the association between physician network properties and health care spending, utilization, and quality of care among Medicare beneficiaries. Design, Setting, and Participants In this cross-sectional study, we ap...
Article
Objective To assess the association between food insecurity and depression symptom severity stratified by sex, and test for evidence of effect modification by social network characteristics. Design A population-based cross-sectional study. The nine-item Household Food Insecurity Access Scale captured food insecurity. Five name generator questions...
Article
Background: Magnetic resonance imaging (MRI) and positron emission tomography (PET) scans are widely used in breast cancer practice despite unproven benefits. We examined the extent to which social contagion is associated with adoption of these imaging modalities. Methods: We used Surveillance, Epidemiology, and End Results-Medicare to construct...
Conference Paper
Full-text available
Antibiotic-resistant organisms, an increasing source of morbidity and mortality, have a natural reservoir in hospitals, and recent estimates suggest that almost 2 million people develop hospital-acquired infections each year in the US alone. We investigate the temporal network of transfers of Medicare patients across US hospitals over a 2-year peri...
Article
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Antibiotic-resistant bacterial infections are a substantial source of morbidity and mortality and have a common reservoir in inpatient settings. Transferring patients between facilities could be a mechanism for the spread of these infections. We wanted to assess whether a network of hospitals, linked by inpatient transfers, contributes to the sprea...
Article
Coordination in groups faces a sub-optimization problem and theory suggests that some randomness may help to achieve global optima. Here we performed experiments involving a networked colour coordination game in which groups of humans interacted with autonomous software agents (known as bots). Subjects (n = 4,000) were embedded in networks (n = 230...
Article
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Numerous models explore how a wide variety of biological and social phenomena spread in social networks. However, these models implicitly assume that the spread of one phenomenon is not affected by the spread of another. Here, we develop a model of “dueling contagions”, with a particular illustration of a situation where one is biological (influenz...
Article
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Introduction Despite global progress on many measures of child health, rates of neonatal mortality remain high in the developing world. Evidence suggests that substantial improvements can be achieved with simple, low-cost interventions within family and community settings, particularly those designed to change knowledge and behaviour at the communi...
Article
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Two separate bodies of work have examined whether culture affects cooperation in economic games and whether cooperative or non-cooperative decisions occur more quickly. Here, we connect this work by exploring the relationship between decision time and cooperation in American versus Indian subjects. We use a series of dynamic social network experime...
Article
Since the 1970s sociologists have explored the best means for measuring social networks, although few name generator analyses have used sociocentric data or data from developing countries, partly because sociocentric studies in developing countries have been scant. Here, we analyze 12 different name generators used in a sociocentric network study c...
Article
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Face-to-face social interactions enhance well-being. With the ubiquity of social media, important questions have arisen about the impact of online social interactions. In the present study, we assessed the associations of both online and offline social networks with several subjective measures of well-being. We used 3 waves (2013, 2014, and 2015) o...
Article
Social interactions increasingly take place online. Friendships and other offline social ties have been repeatedly associated with human longevity, but online interactions might have different properties. Here, we reference 12 million social media profiles against California Department of Public Health vital records and use longitudinal statistical...
Article
Variations in opinion between members of a community can be exploited to facilitate desirable changes in attitude, as exemplified by films that explore different beliefs about female genital cutting. See Letter p.506
Article
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Intergroup violence is common among humans worldwide. To assess how within-group social dynamics contribute to risky, between-group conflict, we conducted a 3-y longitudinal study of the formation of raiding parties among the Nyangatom, a group of East African nomadic pastoralists currently engaged in small-scale warfare. We also mapped the social...
Article
Socially isolated individuals face elevated rates of illness and death. Conventional measures of social connectedness reflect an individual’s perceived network and can be subject to bias and variation in reporting. In this study of a large human social network, we find that greater indegree, a sociocentric measure of friendship and familial ties id...
Article
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Are cooperative decisions typically made more quickly or slowly than non-cooperative decisions? While this question has attracted considerable attention in recent years, most research has focused on one-shot interactions. Yet it is repeated interactions that characterize most important real-world social interactions. In repeated interactions, the c...
Article
Objective: This study evaluated whether desiring to lose weight is associated with subsequent changes in social contact with individuals perceived to be thinner or heavier. Methods: Longitudinal data were used to examine associations between desiring to lose weight at baseline and social contact with thinner and heavier individuals across a 1-ye...
Article
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Background Intimate partner violence (IPV) is a complex global problem, not only because it is a human rights issue, but also because it is associated with chronic mental and physical illnesses as well as acute health outcomes related to injuries for women and their children. Attitudes, beliefs, and norms regarding IPV are significantly associated...
Article
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There is significant heterogeneity within and between populations in their propensity to engage in conflict. Most research has neglected the role of within-group effects in social networks in contributing to between-group violence and focused instead on the precursors and consequences of violence, or on the role of between-group ties. Here, we expl...