Tom A B Snijders

Tom A B Snijders
University of Groningen | RUG · Department of Sociology

PhD, Maths, U Groningen, 1979

About

197
Publications
97,618
Reads
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30,863
Citations
Additional affiliations
October 2006 - present
University of Oxford
Position
  • Professor of Statistics in the Social Sciences
September 2001 - present
University of Groningen
Position
  • Professor (Full)
Education
September 1967 - May 1979
University of Groningen
Field of study
  • Mathematics

Publications

Publications (197)
Article
Full-text available
Longitudinal studies of criminal networks are rare yet necessary to assess the adaptation and recovery of criminal networks after disruptions. We study the structural and individual effects of law enforcement disruption on criminal networks using longitudinal data on two Dutch jihadi networks (n1 = 57; n2 = 26). We expect that actors in criminal ne...
Article
We review the empirical comparison of Stochastic Actor-oriented Models (SAOMs) and Temporal Exponential Random Graph Models (TERGMs) by Leifeld & Cranmer in this journal [Network Science 7(1):20–51, 2019]. When specifying their TERGM, they use exogenous nodal attributes calculated from the outcome networks’ observed degrees instead of endogenous ER...
Preprint
Stochastic actor-oriented models (SAOM) are a broadly applied modelling framework for analysing network dynamics using network panel data. They have been extended to address co-evolution of multiple networks as well as networks and behaviour. This paper extends the SAOM to the analysis of multiple network panels through a random coefficient multile...
Article
Full-text available
Background Despite the steady growth of sexual transmission of HIV, there is little evidence about safe sexual behavior of FSWs, and social network effects on this behavior, in Iran. Our aim in this study was to determine the effect of social network characteristics on condom use among FSWs, considering individual characteristics of the FSWs and of...
Article
Full-text available
Background Despite the widespread knowledge about social support and health, there is little information about the association between social support and HIV risk behaviors such as condom use among female sex workers (FSWs) in Iran. This study aimed to determine the association between social support and frequency of condom use among FSWs in Tehran...
Poster
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More than a decade has passed since the introduction of relational event models, which are statistical models for the analysis of sequenced or time-stamped dyadic network data (Butts, 2008). Relational event data can be collected or found in various contexts, for example, in social media networks, communication networks, organizational networks, po...
Preprint
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Despite the central role of self-assembled groups in animal and human societies, statistical tools to explain their composition are limited. We introduce a statistical framework for cross-sectional observations of groups with exclusive membership to illuminate the social and organizational mechanisms that bring people together. Drawing from stochas...
Article
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This paper compares several missing data treatment methods for missing network data on a diverse set of simulated networks under several missing data mechanisms. We focus the comparison on three different outcomes: descriptive statistics, link reconstruction, and model parameters. The results indicate that the often used methods (analysis of availa...
Preprint
Full-text available
We review the empirical comparison of SAOMs and TERGMs by Leifeld and Cranmer (2019) in Network Science. We note that their model specification uses nodal covariates calculated from observed degrees instead of using structural effects, thus turning endogeneity into circularity. In consequence, their out-of-sample predictions using TERGMs are based...
Article
Background: An adequate perception of the degree to which one is at risk of having or contracting HIV is necessary for behavioural change and the adoption of safe behaviours. There are limited data regarding HIV risk perceptions among female sex workers in Iran. This study aimed to determine the HIV risk perception status and its association with s...
Article
This paper proposes that common measures for network transitivity, based on the enumeration of transitive triples, do not reflect the theoretical statements about transitivity they aim to describe. These statements are often formulated as comparative conditional probabilities, but these are not directly reflected by simple functions of enumerations...
Article
Full-text available
The present study is an analysis of a Czech political corruption network known as the Rath affairreconstructed with publicly available data. We argue that for the study of criminal networks it is fruitful tofollow a multiplex approach, i.e., to distinguish several interdependent network dimensions and study howthey are interrelated. Relational elem...
Article
Full-text available
Using data on 32 actors and ties among them drawn from available court files, we combine analytical sociology with statistical models for networks in order to analyse a case of a counterfeit alcohol distribution network from the Czech Republic. We formulate a theory of action and identify relational mechanisms which could explain how the structure...
Article
Stochastic actor-oriented models (SAOMs) can be used to analyse dynamic network data, collected by observing a network and a behaviour in a panel design. The parameters of SAOMs are usually estimated by the method of moments (MoM) implemented by a stochastic approximation algorithm, where statistics defining the moment conditions correspond in a na...
Article
Full-text available
The dynamics of individual behavior are related to the dynamics of the social structures in which individuals are embedded. This implies that in order to study social mechanisms such as social selection or peer influence, we need to model the evolution of social networks and the attributes of network actors as interdependent processes. The stochast...
Article
Full-text available
The aim of this study was to unravel the interrelatedness of friendship and help, and to examine the characteristics of friendship and help networks. The effects of mutual versus one‐sided help relations on friendship initiation and maintenance, and vice versa, were examined. Friendship and help networks were analyzed (N = 953 students; 41 classroo...
Article
Full-text available
We consider the specification of effects of numerical actor attributes, having an interval level of measurement, in statistical models for directed social networks. A fundamental mechanism is homophily or assortativity, where actors have a higher likelihood to be tied with others having similar values of the variable under study. But there are othe...
Article
Full-text available
This study investigated if and how children and teachers differ in their assessment of victim‐aggressor relationships in kindergartens. Self‐, peer, and teacher reports of victimization‐aggression networks (who is victimized by whom) were investigated in 25 Swiss kindergartens with 402 5‐ to 7‐years‐old. It was examined whether child characteristic...
Article
Objectives: The aim of the present study was to develop and validate a safe sex norm questionnaire as an appropriate instrument which would be adaptable to the female sex worker (FSW) population. Study design: A mixed method study. Methods: Appropriate content was prepared through a literature review. Content validation indices were assessed u...
Article
Full-text available
Background: Social network characteristics have an important role in understanding HIV transmission among female sex workers. The purpose of this systematic review was to summarize and critically appraise the existing studies on the social network characteristics and HIV risk behaviors among female sex workers. Method: A systematic review was pe...
Conference Paper
Full-text available
This paper compares several imputation methods for missing data in network analysis on a diverse set of simulated networks under several missing data mechanisms. Previous work has highlighted the biases in descriptive statistics of networks introduced by missing data. The results of the current study indicate that the default methods (analysis of a...
Article
We examined social mechanisms that account for similarity in the social context of school-sponsored extracurricular sports activities among friends. We distinguish two social mechanisms: “shared sports activities that lead to friendship,” whereby friendship formation and maintenance are conditioned by joint sports participation, and “friendship tha...
Article
Full-text available
Longitudinal social network studies can easily suffer from insufficient statistical power. Studies that simultaneously investigate change of network ties and change of nodal attributes (selection and influence studies) are particularly at risk because the number of nodal observations is typically much lower than the number of observed tie variables...
Article
Full-text available
We consider the specification of effects of numerical actor attributes in statistical models for directed social networks. A fundamental mechanism is homophily or assortativity, where actors have a higher likelihood to be tied with others having similar values of the variable under study. But there are other mechanisms that may also play a role in...
Article
Full-text available
Missing data on network ties are a fundamental problem for network analysis. The biases induced by missing edge data are widely acknowledged. In this paper, we present a new method with two variants to handle missing data due to actor non-response in the framework of stochastic actor-oriented models (SAOMs). The proposed method imputes missing tie...
Chapter
In some panel data studies, respondents are nested in social contexts, like classrooms or organizations. The social relations, such as friendship or collaboration, between the individuals in such contexts can be represented by social networks. Like individual outcomes (e.g., behavior or performance), the social relations between individuals are not...
Article
Social networks and the attributes of the actors in these networks are not static; they may develop interdependently over time. The stochastic actororiented model allows for statistical inference on the mechanisms driving this co-evolution process. In earlier versions of this model, dynamic actor attributes are assumed to be measured on an ordinal...
Article
Full-text available
Social relations are multiplex by nature: actors in a group are tied together by various types of relationships. To understand and explain group processes it is, therefore, important to study multiple social networks simultaneously in a given group. However, with multiplexity the complexity of data also increases. Although some multivariate network...
Article
This article discusses the stochastic actor-oriented model for analyzing panel data of networks. The model is defined as a continuous-time Markov chain, observed at two or more discrete time moments. It can be regarded as a generalized linear model with a large amount of missing data. Several estimation methods are discussed. After presenting the m...
Article
In this study, we examined the dynamics of the perception of “dislike” ties (reputational dislike) among adolescents within the contexts of friendship, perceived popularity, substance use, and Facebook use. Survey data were collected from a longitudinal sample of 238 adolescents from the 11th and 12th grades in one California high school. We estima...
Article
Full-text available
Two approaches for the statistical analysis of social network generation are widely used; the tie-oriented exponential random graph model (ERGM) and the stochastic actor-oriented model (SAOM) or Siena model. While the choice for either model by empirical researchers often seems arbitrary, there are important differences between these models that cu...
Article
This paper examines the collaboration structures and dynamics of the co-authorship network of all Slovenian researchers. Its goal is to identify the key factors driving collaboration and the main differences in collaboration behavior across scientific fields and disciplines. Two approaches to modelling network dynamics are combined in this paper: t...
Article
Stochastic actor-based models for network dynamics have the primary aim of statistical inference about processes of network change, but may be regarded as a kind of agent-based models. Similar to many other agent-based models, they are based on local rules for actor behavior. Different from many other agent-based models, by including elements of ge...
Article
Full-text available
Antisocial behavior typically increases during early adolescence, but the possibility of seasonal variation has not been examined. In this study, trajectories of antisocial behavior were estimated for early adolescent boys and girls. Data were obtained from a 3-year longitudinal study of 11 middle schools in the western United States (n = 5,742), w...
Article
In the present paper, the quality of the Eritrean Secondary Education Certificate Examinations (ESECE) has been evaluated by investigating the reliability of its two compulsory parts – the English Language and Mathematics tests. An item analysis has also been done. In view of the low correlations between its subtest scores, the English language exa...
Article
A complete survey of a network in a large population may be prohibitively difficult and costly. So it is important to estimate models for networks using data from various network sampling designs, such as link-tracing designs. We focus here on snowball sampling designs, designs in which the members of an initial sample of network members are asked...
Article
A novel version of Snijders's stochastic actor-based modeling (SABM) framework is applied to model the diffusion of first alcohol use through middle school-wide longitudinal networks of early adolescents, aged approximately 11-14 years. Models couple a standard SABM for friendship network evolution with a proportional hazard model for first alcohol...
Article
Full-text available
We propose a new stochastic actor-oriented model for the co-evolution of two-mode and one-mode networks. The model posits that activities of a set of actors, represented in the two-mode network, co-evolve with exchanges and interactions between the actors, as represented in the one-mode network. The model assumes that the actors, not the activities...
Book
The Handbook of Rational Choice Social Research offers the first comprehensive overview of how the rational choice paradigm can inform empirical research within the social sciences. This landmark collection highlights successful empirical applications across a broad array of disciplines, including sociology, political science, economics, history, a...
Article
Bilateral trade agreements have proliferated rapidly within the last two decades, growing into a dense network of multiple ties between countries. The spread of preferential trade agreements (PTAs), however, is not uniform: some countries have signed a multitude of deals, while others remain much less involved. This article presents a longitudinal...
Article
Full-text available
In traditional studies on value-added indicators of educational effectiveness, students are usually treated as belonging to those schools where they took their final examination. However, in practice, students sometimes attend multiple schools and therefore it is questionable whether this assumption of belonging to the last school they attended can...
Article
Geographic proximity is a determinant factor of friendship. Friendship datasets that include detailed geographic information are scarce, and when this information is available, the dependence of friendship on distance is often modelled by pre-specified parametric functions or derived from theory without further empirical assessment. This paper aims...
Article
This article examines the dynamics of peer relationships across the first 2 grades of Dutch junior high schools (average age 13–14). Specifically, we studied how gender and compositional changes in classrooms structured the changes in peer relationships between the 2 grades. Expectations were derived from past research, and we tested whether these...
Article
Full-text available
Statistical models for social networks as dependent variables must represent the typical network dependencies between tie variables such as reciprocity, homophily, transitivity, etc. This review first treats models for single (cross-sectionally observed) networks and then for network dynamics. For single networks, the older literature concentrated...
Article
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This article examines the use of various research designs in the social sciences as well as the choices that are made when a quasi-experimental design is used. A content analysis was carried out on articles published in 18 social science journals with various impact factors. The presence of quasi-experimental studies was investigated as well as cho...
Chapter
Multilevel Analysis, Hierarchical Linear ModelsThe term “Multilevel Analysis” is mostly used interchangeably with “Hierarchical Linear Modeling,” although strictly speaking these terms are distinct. Multilevel Analysis may be understood to refer broadly to the methodology of research questions and data structures that involve more than one type of...
Article
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This research is part of the Research Program “Creation of and returns to social capital; Social
Article
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Abstract A multilevel approach is proposed to the study of the evolution of multiple networks. In this approach, the basic evolution process is assumed to be the same, while parameter values may dier between different networks. For the network evolution process, stochastic actororiented models are used, of which the parameters are estimated by Mark...
Article
Full-text available
For exponential random graph models, under quite general conditions, it is proved that induced subgraphs on node sets disconnected from the other nodes still have distributions from an exponential random graph model. This can help in the theoretical interpretation of such models. An application is that for saturated snowball samples from a potentia...
Article
A recurrent problem in the analysis of behavioral dynamics, given a simultaneously evolving social network, is the difficulty of separating the effects of partner selection from the effects of social influence. Because misattribution of selection effects to social influence, or vice versa, suggests wrong conclusions about the social mechanisms unde...
Article
Full-text available
The major aim of the treatment of forensic psychiatric patients is to reduce risk of future violence by means of a positive change in the factors associated with the offence. In this article, we argue that information on patients' social network patterns and the content of their relationships provide detailed information about relational behavior t...
Article
The main goal of this study was to examine differences between adolescent male and female friendship networks regarding smoking-based selection and influence processes using newly developed social network analysis methods that allow the current state of continuously changing friendship networks to act as a dynamic constraint for changes in smoking...
Article
The mutual influence of smoking behavior and friendships in adolescence is studied. It is attempted to disentangle influence and selection processes in reciprocal and non-reciprocal friendships. An actor-based model is described for the co-evolution of friendship networks and smoking behavior. This model considers alternative selection and influenc...
Article
Positive association of relevant characteristics is a widespread pattern among adolescent friends. A positive association may be caused by the selection of similar others as friends and by the deselection of dissimilar ones, but also by influence processes where friends adjust their behavior to each other. Social control theory argues that adolesce...
Article
Full-text available
Ecosystem components interact in complex ways and change over time due to a variety of both internal and external influences (climate change, season cycles, human impacts). Such processes need to be modeled dynamically using appropriate statistical methods for assessing change in network structure. Herewe use visualizations and statistical models o...
Article
The co-evolution of adolescents' friendship networks and their smoking behavior is examined in a large sample across six European countries. Selection and influence processes are disentangled using new methods of social network analysis that enable alternative selection mechanisms to be controlled for. The sample consisted of 7704 adolescents parti...
Article
Full-text available
With few exceptions, statistical analysis of social networks is currently focused on cross-sectional or panel data. On the other hand, automated collection of network-data often produces event data, i. e., data encoding the exact time of interaction between social actors. In this paper we propose models and methods to analyze such networks of dyadi...
Article
Full-text available
Previous studies offer a limited perspective on the dynamic course of distress in cancer patients and their partners, owing to a restricted number of assessment points and the absence of comparison controls drawn from the general population. This study investigated the course of distress among breast cancer patients and their partners (N = 92 coupl...
Article
Full-text available
Refusal of patients to participate in intervention programs is an important problem in clinical trials but, in general, researchers devote relatively little attention to it. In this article, a comparison is made between patients who, after having been invited, agreed to participate in a self-management intervention (participants) and those who refu...
Article
This paper explores some possibilities for variance reduction by the use of antithetic variates when estimating probabilities.
Article
In biological analysis of behaviour, transition matrices occur of which the diagonal entries are essentially zero. For such transition matrices, a model of randomness is constructed, with a test for the hypothesis that this model holds.
Article
We consider a continuous-time model for the evolution of social networks. A social network is here conceived as a (di-) graph on a set of vertices, representing actors, and the changes of interest are creation and disappearance over time of (arcs) edges in the graph. Hence we model a collection of random edge indicators that are not, in general, in...
Article
This study investigated the effects of general practitioner, patient, and prescription characteristics on the reduction of long-term benzodiazepine prescribing by sending a letter to chronic users. The data were analyzed with a method respecting the hierarchical data structure. Data were obtained from 8,170 chronic users nested in 147 general pract...
Article
This paper describes an empirical comparison of four specifications of the exponential family of random graph models (ERGM), distinguished by model specification (dyadic independence, Markov, partial conditional dependence) and, for the Markov model, by estimation method (Maximum Pseudolikelihood, Maximum Likelihood). This was done by reanalyzing 1...
Article
Relational approaches to organization typically ignore processes of network formation while studying network consequences, and, symmetrically, ignore the implications of network structures and flows while studying network antecedents. In this paper we address these symmetric weaknesses in the organizational literature on networks consequences and a...
Article
Full-text available
Actor-oriented models are described as a longitudinal strategy for examining the co-evolution of social networks and individual behaviors.We argue that these models provide advantages over conventional approaches due to their ability to account for inherent dependencies between individuals embedded in a social network (i.e., reciprocity, transitivi...
Article
Many chronically ill older patients in the Netherlands have a combination of more than one chronic disease. There is therefore a need for self-management programs that address general management problems, rather than the problems related to a specific disease. The Chronic Disease Self-Management Program (CDSMP) seems to be very suitable for this pu...
Article
This article reviews new specifications for exponential random graph models proposed by Snijders et al. [Snijders, T.A.B., Pattison, P., Robins, G.L., Handcock, M., 2006. New specifications for exponential random graph models. Sociological Methodology] and demonstrates their improvement over homogeneous Markov random graph models in fitting empiric...