ORCID Profile
0000-0003-3157-4157
Current Organisations
Nuffield College, University of Oxford
,
University of Groningen
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Publisher: SAGE Publications
Date: 18-04-2012
Abstract: 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 network analysis method to analyze the patterns of the formation of trade agreements, based on the mutual codetermination of network structure and agreement formation. The findings suggest that PTAs spread endogenously because of structural arbitrage effects in the network, and that they establish a hierarchy among countries. Rich countries form ties with each other and middle-income countries, who themselves create a horizontal layer of PTAs, but least-developed countries are left behind and do not form many ties. Supplanting the multilateral trade regime with preferential agreements therefore creates a system of highly asymmetrical relationships of weaker spokes around a few hubs.
Publisher: Wiley
Date: 16-01-2008
Publisher: Institute of Mathematical Statistics
Date: 06-2010
DOI: 10.1214/09-AOAS313
Publisher: Elsevier BV
Date: 07-2012
Publisher: Wiley
Date: 08-06-2010
DOI: 10.1111/J.1360-0443.2010.02930.X
Abstract: 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 behaviour, while allowing current smoking behaviour to be simultaneously a dynamic constraint for changes in friendship networks. Longitudinal design with four measurements. Nine junior high schools in Finland. A total of 1163 adolescents (mean age = 13.6 years) who participated in the control group of the ESFA (European Smoking prevention Framework Approach) study, including 605 males and 558 females. Smoking behaviour of adolescents, parents, siblings and friendship ties. Smoking-based selection of friends was found in male as well as female networks. However, support for influence among friends was found only in female networks. Furthermore, females and males were both influenced by parental smoking behaviour. In Finnish adolescents, both male and female smokers tend to select other smokers as friends but it appears that only females are influenced to smoke by their peer group. This suggests that prevention c aigns targeting resisting peer pressure may be more effective in adolescent girls than boys.
Publisher: Informa UK Limited
Date: 27-07-2010
Publisher: Springer Science and Business Media LLC
Date: 07-04-2015
DOI: 10.1007/S11192-015-1585-7
Abstract: 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: the small-world model and the mechanism of preferential attachment, also known as the process of cumulative advantage. Stochastic-actor-based modelling of co-authorship network dynamics uses data for the complete longitudinal co-authorship networks for the entire Slovenian scientific community from 1996 to 2010. We confirmed the presence of clustering in all fields and disciplines. Preferential attachment is far more complex than a single global mechanism. There were two clear distinctions regarding collaboration within scientific fields and disciplines. One was that some fields had an internal national saturation inhibiting further collaboration. The second concerned the differential impact of collaboration with scientists from abroad on domestic collaboration. In the natural, technical, medical, and biotechnical sciences, this promotes collaboration within the Slovenian scientific community while in the social sciences and humanities this inhibits internal collaboration.
Publisher: Cambridge University Press (CUP)
Date: 08-05-2023
DOI: 10.1017/NWS.2023.9
Abstract: Relational event models (REMs) for the analysis of social interaction were first introduced 15 years ago. Since then, a number of important substantive and methodological contributions have produced their progressive refinement and hence facilitated their increased adoption in studies of social and other networks. Today REMs represent a well-established class of statistical models for relational processes. This special issue of Network Science demonstrates the standing and recognition that REMs have achieved within the network analysis and networks science communities. We wrote this brief introductory editorial essay with four main objectives in mind: (i) positioning relational event data and models in the larger context of contemporary network science and social network research (ii) reviewing some of the most important recent developments (iii) presenting the innovative studies collected in this special issue as evidence of the empirical value of REMs, and (iv) identifying open questions and future research directions.
Publisher: Elsevier BV
Date: 2017
Publisher: Informa UK Limited
Date: 09-2001
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: IEEE
Date: 08-2018
Publisher: Springer International Publishing
Date: 16-12-2016
Publisher: Elsevier BV
Date: 11-2009
DOI: 10.1016/J.SOCSCIMED.2009.08.003
Abstract: The co-evolution of adolescents' friendship networks and their smoking behavior is examined in a large s le 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 s le consisted of 7704 adolescents participating in the control group of the ESFA (European Smoking prevention Framework Approach) study. The design was longitudinal with four observations. The main measurements were friendship ties, adolescents smoking behavior, parental smoking behavior, and sibling smoking behavior. Results indicated that in each country adolescents preferred selecting friends based on similar smoking behavior. Support for the influence of friends was found in only two countries. A similarity in smoking behavior between friends was explained more strongly by smoking-based selection processes than by the influence of friends in each of the six countries. Prevention programs need to address aspects that drive peer selection, and reinforce non-smoking attitudes in adolescents.
Publisher: Elsevier BV
Date: 05-2005
DOI: 10.1016/J.YHBEH.2005.01.004
Abstract: Social support has a positive influence on the course of a depression and social housing of rats could provide an animal model for studying the neurobiological mechanisms of social support. Male and female rats were subjected to chronic footshock stress for 3 weeks and pair-housing of rats was used to mimic social support. Rats were isolated or housed with a partner of the opposite sex. A plastic tube was placed in each cage and subsequently used as a 'safe' area in an open field test. Time spent in the tube was used as a measurement of anxiety levels. Chronic stress increased adrenal weights in all groups, except for isolated females who showed adrenal hypertrophy in control conditions. In isolated males, chronic stress resulted in an increase in the time the animals spent in the tube. While stress did not affect this parameter in socially housed males, males with a stressed partner showed a similar response as isolated stressed males. Even though adrenal weights showed that isolated females were more affected by stress, after chronic stress exposure, they spent less time in the tube than socially housed females. Socially housed stressed females spent less time in the 'safe' tube compared to control counterparts, indicating that stress has a gender-specific behavioral effect. pair-housing had a stress-reducing effect on behavior in males. Isolation of females was stressful by itself. Pair housing of females was not able to prevent stress-induced behavioral changes completely, but appeared to reduce the effects of chronic stress.
Publisher: Elsevier BV
Date: 12-1990
Publisher: Elsevier BV
Date: 11-2011
Publisher: Elsevier BV
Date: 2010
Publisher: Elsevier BV
Date: 2010
Publisher: Elsevier BV
Date: 12-2006
Publisher: Elsevier BV
Date: 12-2007
Publisher: Springer Science and Business Media LLC
Date: 1997
Publisher: Springer Science and Business Media LLC
Date: 09-1991
DOI: 10.1007/BF02294482
Publisher: Edward Elgar Publishing
Date: 10-06-2022
Publisher: Cambridge University Press (CUP)
Date: 09-2019
DOI: 10.1017/NWS.2019.32
Abstract: 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. We think that a better approach is obtained by considering the probability of a tie between two randomly drawn nodes, conditional on selected features of the network. Two measures of transitivity based on correlation coefficients between the existence of a tie and the existence, or the number, of two-paths between the nodes are developed, and called “Transitivity Phi” and “Transitivity Correlation.” Some desirable properties for these measures are studied and compared to existing clustering coefficients, in both random (Erdös–Renyi) and in stylized networks (windmills). Furthermore, it is shown that in a directed graph, under the condition of zero Transitivity Correlation, the total number of transitive triples is determined by four underlying features: size, density, reciprocity, and the covariance between in- and outdegrees. Also, it is demonstrated that plotting conditional probability of ties, given the number of two-paths, provides valuable insights into empirical regularities and irregularities of transitivity patterns.
Publisher: Elsevier BV
Date: 2005
Publisher: Wiley
Date: 02-2009
Publisher: Wiley
Date: 18-09-2001
DOI: 10.1002/MPO.1216
Abstract: Children treated for acute lymphoblastic leukemia (ALL) often complain about handwriting problems. Using a computerized writing task, we have prospectively studied the processes necessary for the production of handwriting movements in 11 children (5-12 years old) during treatment for ALL. Children were tested at time points closely related to the vincristine administration. Children treated for ALL drew slower, with longer pause durations and increased drawing pressure. Children were able to overcome the problems, except for a consistently increased drawing pressure. This increased drawing pressure may be an attempt of the children to obtain sufficient kinesthetic information and thus can be seen as an adequate adaptation mechanism in case of peripheral neuropathy due to the neurotoxic effects of vincristine. However, neurotoxic effects of other cytostatic drugs cannot be excluded.
Publisher: SAGE Publications
Date: 11-2003
Abstract: Markov chains can be used for the modeling of complex longitudinal network data. One class of probability models to model the evolution of social networks are stochastic actor-oriented models for network change proposed by Snijders. These models are continuous-time Markov chain models that are implemented as simulation models. The authors propose an extension of the simulation algorithm of stochastic actor-oriented models to include networks of changing composition. In empirical research, the composition of networks may change due to actors joining or leaving the network at some point in time. The composition changes are modeled as exogenous events that occur at given time points and are implemented in the simulation algorithm. The estimation of the network effects, as well as the effects of actor and dyadic attributes that influence the evolution of the network, is based on the simulation of Markov chains.
Publisher: SAGE Publications
Date: 07-2007
Abstract: Actor-oriented models are described as a longitudinal strategy for examining the co-evolution of social networks and in idual behaviors. We argue that these models provide advantages over conventional approaches due to their ability to account for inherent dependencies between in iduals embedded in a social network (i.e., reciprocity, transitivity) and model interdependencies between network and behavioral dynamics. We provide a brief explanation of actor-oriented processes, followed by a description of parameter estimates, model specification, and selection procedures used by the Simulation Investigation for Empirical Network Analyses (SIENA) software program (Snijders, Steglich, Schweinberger, & Huisman, 2006). To illustrate the applicability of these models, we provide an empirical ex le investigating the co-evolution of friendship networks and delinquent behaviors in a longitudinal s le of Swedish adolescents with the goal of simultaneously assessing selection and influence processes. Findings suggest both processes play a substantive role in the observed dynamics of delinquent behaviors, with influence having a relatively stronger role than selection (especially in reciprocated friendships).
Publisher: Springer International Publishing
Date: 16-12-2016
Publisher: Springer International Publishing
Date: 16-12-2016
Publisher: Oxford University Press (OUP)
Date: 05-1996
Publisher: Springer Science and Business Media LLC
Date: 1998
Publisher: Routledge
Date: 29-09-2017
Publisher: Springer Science and Business Media LLC
Date: 11-11-2021
Publisher: Informa UK Limited
Date: 23-09-2010
Publisher: Elsevier BV
Date: 02-2011
Publisher: Springer Science and Business Media LLC
Date: 06-1981
DOI: 10.1007/BF02293900
Publisher: Institute of Mathematical Statistics
Date: 1977
Publisher: American Educational Research Association (AERA)
Date: 1996
DOI: 10.2307/1165273
Publisher: Springer New York
Date: 2017
Publisher: Springer Science and Business Media LLC
Date: 09-2001
DOI: 10.1007/BF02294437
Publisher: SAGE Publications
Date: 05-2018
Abstract: 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. This article presents a simulation-based procedure to evaluate statistical power of longitudinal social network studies in which stochastic actor-oriented models are to be applied. Two detailed case studies illustrate how statistical power is strongly affected by network size, number of data collection waves, effect sizes, missing data, and participant turnover. These issues should thus be explored in the design phase of longitudinal social network studies.
Publisher: Elsevier BV
Date: 12-2020
Publisher: Wiley
Date: 16-09-2010
Publisher: Cambridge University Press (CUP)
Date: 08-06-2018
DOI: 10.1017/NWS.2018.11
Abstract: 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 that leads to shared sports activities,” a form of social influence whereby adolescents join or maintain certain sports activities based on their friends' choices. Using a longitudinal s le of 1,776 10th graders at five high schools in Southern California, we employed a stochastic actor-oriented multivariate dynamic model to model the dynamic interplay between the two-mode affiliation network of adolescents' participation in sports activities and the one-mode friendship network. As a corresponding descriptive method, we propose a quantitative measure for the relative strength of the two-mentioned mechanisms as explanations of the association between the one-mode and the two-mode network. Further, we introduce two specifications that represent homophily effects in the two-mode network and apply them to test gender homophily in sports participation. The results provide strong evidence for both mechanisms, with friendship leading to shared sport activities as stronger than shared sports activities leading to friendships in explaining adolescents' friendships with co-participants.
Publisher: Springer Science and Business Media LLC
Date: 22-03-2018
Publisher: Wiley
Date: 02-2005
Publisher: Elsevier BV
Date: 09-2019
Publisher: Springer Science and Business Media LLC
Date: 07-08-2007
Publisher: SAGE Publications
Date: 09-05-2019
Abstract: The dynamics of in idual behavior are related to the dynamics of the social structures in which in iduals 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 stochastic actor-oriented model is a statistical approach to study network-attribute coevolution based on longitudinal data. In its standard specification, the coevolving actor attributes are assumed to be measured on an ordinal categorical scale. Continuous variables first need to be discretized to fit into such a modeling framework. This article presents an extension of the stochastic actor-oriented model that does away with this restriction by using a stochastic differential equation to model the evolution of a continuous attribute. We propose a measure for explained variance and give an interpretation of parameter sizes. The proposed method is illustrated by a study of the relationship between friendship, alcohol consumption, and self-esteem among adolescents.
Publisher: Oxford University Press
Date: 06-03-2017
DOI: 10.1093/OXFORDHB/9780190228217.013.10
Abstract: Stochastic Actor Oriented Models for Network Dynamics are used for the statistical analysis of longitudinal network data collected as a panel. The probability model defines an unobserved stochastic process of tie changes, where social actors add new ties or drop existing ties in response to the current network structure the panel observations are snapshots of the resulting changing network. The statistical analysis is based on computer simulations of this process, which provides a great deal of flexibility in representing data constraints and dependence structures. In this Chapter we begin by defining the basic model. We then explicate a new model for nondirected ties, including several options for the specification of how pairs of actors coordinate tie changes. Next, we describe coevolution models. These can be used to model the dynamics of several interdependent sets of variables, such as the analysis of panel data on a network and the behavior of the actors in the network, or panel data on two or more networks. We finish by discussing the differences between Stochastic Actor Oriented Models and some other longitudinal network models. A major distinguishing feature is the treatment of time, which allows straightforward application of the model to panel data with different time lags between waves. We provide a variety of applications in political science throughout.
Publisher: SAGE Publications
Date: 07-08-2020
Abstract: This study examines ethnic integration in secondary school. Social identity theory suggests that perception of relevant in idual attributes plays a crucial role in defining ingroups and outgroups, contributing to befriending, and disliking others. Therefore, we analyze the role of peer-perceived ethnicity in social ties. Networks of friendship, dislike, and perceived ethnicity were modeled together using dynamic stochastic actor-oriented models, separating the effect of perceived ethnicity on social ties from that of social ties on perceived ethnicity. Data came from a Hungarian s le of 12 school classes with one minority group: the Roma. Treating friendship and dislike as mutually exclusive and comparing them to neutral relations, we found evidence for the role of perceived ethnicity in dislike—majority students disliked those they perceived as minority peers. However, we saw no direct effect of ethnicity on the friendship network. Implications of the joint modeling of mutually exclusive relationship aspects are discussed.
Publisher: SAGE Publications
Date: 08-2003
DOI: 10.1111/J.0081-1750.2003.00134.X
Abstract: A class of statistical models is proposed that aims to recover latent settings structures in social networks. Settings may be regarded as clusters of vertices. The measurement model is based on two assumptions. (1) The observed network is generated by hierarchically nested latent transitive structures, expressed by ultrametrics, and (2) the expected tie strength decreases with ultrametric distance. The approach could be described as model-based clustering with an ultrametric space as the underlying metric to capture the dependence in the observations. Bayesian methods as well as maximum-likelihood methods are applied for statistical inference. Both approaches are implemented using Markov chain Monte Carlo methods.
Publisher: American Educational Research Association (AERA)
Date: 06-2001
DOI: 10.3102/10769986026002133
Abstract: Available variance component tests are reviewed and three new score tests are presented. In the first score test, the asymptotic normal distribution of the test statistic is used as a reference distribution. In the other two score tests, a Satterthwaite approximation is used for the null distribution of the test statistic. We evaluate the performance of the score tests and other available tests by means of a Monte Carlo study. The new tests are computationally relatively cheap and have good power properties.
Publisher: Springer Science and Business Media LLC
Date: 03-1990
DOI: 10.1007/BF01889701
Publisher: Elsevier BV
Date: 04-1998
Publisher: Springer Science and Business Media LLC
Date: 12-1986
DOI: 10.1007/BF02295597
Publisher: Springer Science and Business Media LLC
Date: 24-01-2023
DOI: 10.1007/S41109-023-00535-W
Abstract: The study investigates to what degree Indonesia’s large-scale decentralization and democratization changed corruption networks. A role structure approach is developed to move current analysis of dyad-level structures to the network level. This approach is empirically tested by comparing the relational content and third-party structures of 96 corruption networks operating in the first phase of decentralization (2001–2004), characterized by a powerful local council, with 94 corruption networks detected in the second phase (2005–2013), when direct local elections were introduced, and the power of the local council declined. Building on Fiske’s relational model theory, it is argued and found that the local executive’s reduced dependence on the local council provided the opportunity to initiate corrupt exchanges with a broader set of players both inside and outside the bureaucracy. Whereas deep dependence power relations (i.e. formal authority) remained important, an increasing proportion of corruption networks involved compound role structures characterized by both shallow (non-embedded profit and work relations) and deep interdependence (kin- and friendship). Furthermore, third party intermediaries became more important. Implications for the study of networks of corruption are discussed.
Publisher: SAGE Publications
Date: 30-01-2023
DOI: 10.1177/00811750221145166
Abstract: Despite the central role of self-assembled groups in animal and human societies, statistical tools to explain their composition are limited. The authors 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 stochastic models for networks and partitions, the proposed framework introduces an exponential family of distributions for partitions. The authors derive its main mathematical properties and suggest strategies to specify and estimate such models. A case study on hackathon events applies the developed framework to the study of mechanisms underlying the formation of self-assembled project teams.
Publisher: SAGE Publications
Date: 2001
Publisher: Elsevier BV
Date: 03-1999
Publisher: Elsevier BV
Date: 06-1997
DOI: 10.1016/S0001-6918(96)00047-9
Abstract: This study reports on central and peripheral determinants of timing variability in self-paced tapping by children with early-treated congenital hypothyroidism (CH). A theoretical model of the timing of repetitive movements developed by Wing and Kristofferson was applied to estimate the central timekeeper (clock) and peripheral implementation (motor delay) variances from the variability in the response intervals. Before it is diagnosed and treated, CH is known to affect proper development of the cerebellum. If this would affect the time-keeper function of the cerebellum, it should be reflected by an increased central clock variability rather than by an increased peripheral motor-delay variability in terms of the Wing and Kristofferson model. Results of 46 children with early-treated CH, differing in severity (21 severe, 25 mild), and 34 normal controls are reported. A refinement of the Wing and Kristofferson model is applied to estimate central clock and peripheral motor delay timing variability more precisely than has been done before. Results show that for children with early-treated CH the estimate of the motor delay variance is four times higher than for the controls, while the estimate of the clock variance does not differ between the groups. It is concluded that motor problems in early-treated CH are associated with peripheral rather than with central timing deficiencies.
Publisher: Elsevier BV
Date: 05-2013
Publisher: SAGE Publications
Date: 02-1994
DOI: 10.1177/0049124194022003004
Abstract: The concept of explained proportion of variance or modeled proportion of variance is reviewed in the situation of the random effects hierarchical two-level model. It is argued that the proportional reduction in (estimated) variance components is not an attractive parameter to represent the joint importance of the explanatory (independent) variables for modeling the dependent variable. It is preferable instead to work with the proportional reduction in mean squared prediction error for predicting in idual values (for the modeled variance at level 1) and the proportional reduction in mean squared prediction error for predicting group averages (for the modeled variance at level 2). It is shown that when predictors are added, the proportion of modeled variance defined in this way cannot go down in the population if the model is correctly specified, but can go down in a s le the latter situation then points to the possibility of misspecification. This provides a diagnostic means for identifying misspecification.
Publisher: Informa UK Limited
Date: 22-08-2019
Publisher: Wiley
Date: 11-05-2014
DOI: 10.1111/JORA.12055
Publisher: SAGE Publications
Date: 02-2001
DOI: 10.1177/00131640121971103
Abstract: The unidimensional nature of the De Jong-Gierveld Loneliness Scale is investigated. The internal properties of the scale scores were studied using item response theory, supplemented by an external validity study. In line with the theory of relational loneliness, the results stress the significance of distinguishing between emotional loneliness and social loneliness.
Publisher: Informa UK Limited
Date: 04-2003
Publisher: Elsevier BV
Date: 11-1990
Publisher: Wiley
Date: 05-2002
Abstract: A number of estimation methods for the variance components in the Wing-Kristofferson model for inter-response times are examined and compared by means of a simulation study. The estimation methods studied are the method of moments, maximum likelihood, and an alternative approach in which the Wing-Kristofferson model is recognized as a moving average model.
Publisher: Institute of Mathematical Statistics
Date: 09-1981
Publisher: Elsevier BV
Date: 07-2020
Publisher: Elsevier BV
Date: 05-2007
DOI: 10.1016/J.SOCSCIMED.2007.02.008
Abstract: 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 purpose. In evaluations of the program that have been carried out in the United States and China, positive effects were found on self-management behaviour and health status. However, the program has not yet been evaluated in the Netherlands. Therefore, the aim of this study was to evaluate the short-term and longer-term effects of the program among chronically ill older people in the Netherlands. One hundred and thirty-nine people aged 59 or older, with a lung disease, a heart disease, diabetes, or arthritis were randomly assigned to an intervention group (CDSMP) or a control group (care-as-usual). Demographic data and data on self-efficacy, self-management behaviour and health status were collected at three measurement moments (baseline, after 6 weeks, and after 6 months). The patients who participated rated the program with a mean of 8.5 points (range 0-10), and only one dropped out. However, our study did not yield any evidence for the effectiveness of the CDSMP on self-efficacy, self-management behaviour or health status of older patients in the Netherlands. Because the patients who participated were very enthusiastic, which was also indicated by very high mean attendance (5.6 out of 6 sessions) and only one dropout, it seems too early to conclude that the program is not beneficial for these patients.
Publisher: Elsevier BV
Date: 04-1999
Publisher: Springer Science and Business Media LLC
Date: 25-10-2006
DOI: 10.1007/S10459-006-9038-Y
Abstract: Today's health sciences educational programmes have to deal with a growing and changing amount of knowledge. It is becoming increasingly important for students to be able to use and manage knowledge. We suggest incorporating open-book tests in assessment programmes to meet these changes. This view on the use of open-book tests is discussed and the influence on test quality is examined. To cope with the growing amount of medical knowledge, we have ided the body of knowledge into core knowledge, which students must know without need for references, and backup knowledge, which students need to understand and use properly with the help of references if so desired. As a result, all tests consist of a subtest for reproduction and understanding of core knowledge (a closed-book test) and a subtest for the ability to understand and manage backup knowledge (an open-book test). Statistical data from 14 such double-subtest exams for first and second-year students were analyzed for two cohorts (N = 435 and N = 449) with multilevel analysis, in accordance with generalizability theory. The reliability of the open and closed-book sections of the separate tests varied between 0.712 and 0.850. The open-book items reduce reliability somewhat. The estimated disattenuated correlation was 0.960 and 0.937 for cohorts 1 and 2 respectively. It is concluded that the use of open-book items with closed-book items slightly decreases test reliability but the overall index is acceptable. In addition, open and closed-book sections are strongly positively related. Therefore, open-book tests could be helpful in complementing today's assessment programmes.
Publisher: American Psychological Association (APA)
Date: 2000
Publisher: Institute of Mathematical Statistics
Date: 12-2017
DOI: 10.1214/17-AOAS1037
Publisher: Cambridge University Press (CUP)
Date: 03-2019
DOI: 10.1017/NWS.2018.30
Abstract: 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 other mechanisms that may also play a role in how the attribute values of two actors influence the likelihood of a tie between them. We discuss three additional mechanisms: aspiration, the tendency to send more ties to others having high values attachment conformity, sending more ties to others whose values are close to the “social norm” and sociability, where those having higher values will tend to send more ties generally. These mechanisms may operate jointly, and then their effects will be confounded. We present a specification representing these effects simultaneously by a four-parameter quadratic function of the values of sender and receiver. Flexibility can be increased by a five-parameter extension. We argue that for numerical actor attributes having important effects on directed networks, these specifications may provide an improvement. An illustration is given of dependence of advice ties on academic grades, analyzed by the Stochastic Actor-oriented Model.
Publisher: SAGE Publications
Date: 24-09-2012
Abstract: 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 be made. Furthermore, the schools attended earlier by students might have long-term effects on their subsequent performance. Using data from Dutch primary and secondary schools, multiple membership models and cross classification multilevel models were estimated to explore the effects of student mobility and long-term primary school effects on the estimated value added of secondary schools. Long-term effects of primary schools did not change the estimated value added of secondary schools. On the other hand, allowing students to be a member of multiple secondary schools changed the estimated effectiveness of these schools especially for schools in the middle range of effectiveness.
Publisher: Elsevier BV
Date: 05-2007
Publisher: SAGE Publications
Date: 30-08-2013
Abstract: 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 generalized linear statistical models they aim to be realistic detailed representations of network dynamics in empirical data sets. Statistical parallels to micro–macro considerations can be found in the estimation of parameters determining local actor behavior from empirical data, and the assessment of goodness of fit from the correspondence with network-level descriptives. This article studies several network-level consequences of dynamic actor-based models applied to represent cross-sectional network data. Two ex les illustrate how network-level characteristics can be obtained as emergent features implied by microspecifications of actor-based models.
Publisher: Elsevier BV
Date: 10-2012
Publisher: Elsevier BV
Date: 07-1994
Publisher: Elsevier BV
Date: 10-2007
Publisher: Informa UK Limited
Date: 08-1994
Publisher: Edward Elgar Publishing
Date: 04-11-2022
Publisher: Wiley
Date: 15-06-2010
Publisher: No publisher found
Date: 2000
Publisher: Public Library of Science (PLoS)
Date: 19-12-2018
Publisher: IEEE
Date: 07-2009
Publisher: Wiley
Date: 12-1999
DOI: 10.1002/(SICI)1096-911X(199912)33:6<545::AID-MPO4>3.0.CO;2-Y
Abstract: Daily life motor skills of children with acute lymphoblastic leukemia (ALL) were studied during treatment using the Movement Assessment Battery for Children (Movement ABC). In addition, the possible relation with vincristine treatment was investigated. Seventeen children treated for ALL, aged 4-12 years, were compared to an age- and sex-matched control group. The leukemia group performed more poorly than the control group on both fine and gross motor skills. In looking at the number of children with ALL who scored in the clinical range of the different subtests, problems in balance skills were found to be most pronounced at the end of induction therapy. Remarkably, half a year after reinduction therapy, problems with balance had decreased, whereas the number of children with fine motor problems had increased. A relation between the gross motor problems and vincristine neurotoxicity seems plausible based on a descriptive analysis of the data, but this was not supported statistically.
Publisher: Elsevier BV
Date: 09-1987
Publisher: Elsevier BV
Date: 12-2013
Publisher: Cambridge University Press (CUP)
Date: 25-04-2014
DOI: 10.1017/S0954579414000297
Abstract: The complex interplay between bullying/victimization and defending was examined using a longitudinal social network approach (stochastic actor-based models). The (co)evolution of these relations within three elementary schools (Grades 2–5 at Time 1, ages 8–11, N = 354 children) was investigated across three time points within a year. Most bullies and defenders were in the same grade as the victims, although a substantial number of bullies and defenders were in other grades (most often one grade higher). Defenders were usually of the same gender as the victims, whereas most bullies were boys, with boys bullying both boys and girls. In line with goal-framing theory, multiplex network analyses provided evidence for the social support hypothesis (victims with the same bullies defended each other over time) as well as the retaliation hypothesis (defenders run the risk of becoming victimized by the bullies of the victims they defend). In addition, the analysis revealed that bullies with the same victims defended each other over time and that defenders of bullies initiated harassment of those bullies' victims. This study can be seen as a starting point in unraveling the relationship dynamics among bullying, victimization, and defending networks in schools.
Publisher: SAGE Publications
Date: 08-2017
Publisher: Springer Science and Business Media LLC
Date: 16-08-2018
Publisher: SAGE Publications
Date: 17-11-2016
Abstract: 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 current literature tends to miss. First, the ERGM is defined on the graph level, while the SAOM is defined on the transition level. This allows the SAOM to model asymmetric or one-sided tie transition dependence. Second, network statistics in the ERGM are defined globally but are nested in actors in the SAOM. Consequently, dependence assumptions in the SAOM are generally stronger than in the ERGM. Resulting from both, meso- and macro-level properties of networks that can be represented by either model differ substantively and analyzing the same network employing ERGMs and SAOMs can lead to distinct results. Guidelines for theoretically founded model choice are suggested.
Publisher: American Educational Research Association (AERA)
Date: 09-1993
DOI: 10.3102/10769986018003237
Abstract: The hierarchical linear model approach to a two-level design is considered, some variables at the lower level having fixed and others having random regression coefficients. An approximation is derived to the covariance matrix of the estimators of the fixed regression coefficients (for variables at the lower and the higher level) under the assumption that the s le sizes at either level are large enough. This covariance matrix is expressed as a function of parameters occurring in the model. If a research planner can make a reasonable guess as to these parameters, this approximation can be used as a guide to the choice of s le sizes at either level.
Publisher: Elsevier BV
Date: 08-1997
Publisher: Annual Reviews
Date: 11-08-2011
DOI: 10.1146/ANNUREV.SOC.012809.102709
Abstract: 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 on conditionally uniform models. Various types of latent space models have been developed: for discrete, general metric, ultrametric, Euclidean, and partially ordered spaces. Exponential random graph models were proposed long ago but now are applied more and more thanks to the non-Markovian social circuit specifications that were recently proposed. Modeling network dynamics is less complicated than modeling single network observations because dependencies are spread out in time. For modeling network dynamics, continuous-time models are more fruitful. Actor-oriented models here provide a model that can represent many dependencies in a flexible way. Strong model development is now going on to combine the features of these models and to extend them to more complicated outcome spaces.
Publisher: SAGE Publications
Date: 09-2019
Abstract: We propose a Mahalanobis distance–based Monte Carlo goodness of fit testing procedure for the family of stochastic actor-oriented models for social network evolution. A modified model distance estimator is proposed to help the researcher identify model extensions that will remediate poor fit. A limited simulation study is provided to establish baseline legitimacy for the Mahalanobis distance–based Monte Carlo test and modified model distance estimator. A forward model selection workflow is proposed, and this procedure is demonstrated on a real data set.
Publisher: Elsevier BV
Date: 10-2007
DOI: 10.1016/J.JCLINEPI.2006.11.024
Abstract: 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 practices. One thousand two hundred fifty-six chronic users in 19 general practices received a letter with the advice to reduce or stop the use of benzodiazepines after the general practitioners had attended a course on benzodiazepine use. In a three-level random intercept multilevel regression model, long-term prescribing of benzodiazepines was the dependent variable. The reduction in benzodiazepine prescribing was significantly larger in the intervention than in the control group: 16% after 6 months and 14% after 12 months, respectively. The age of the patient, gender, and the interaction between age and gender were significant. The combination of the duration (long acting or short acting) with the type of benzodiazepine (anxiolytic or hypnotic) was an important pharmacological baseline covariate. The reduction of benzodiazepine prescribing was mainly explained by the letter intervention and in idual patient characteristics. Multilevel analysis was a worthwhile method for application in this study with its unbalanced design.
Publisher: Springer International Publishing
Date: 2016
Publisher: Springer Science and Business Media LLC
Date: 04-09-2011
Publisher: Elsevier BV
Date: 2010
Publisher: Elsevier BV
Date: 11-2009
Publisher: Elsevier BV
Date: 07-2022
Publisher: OpenEdition
Date: 03-1997
DOI: 10.4000/MSH.2749
Publisher: Elsevier BV
Date: 07-2012
Publisher: Elsevier BV
Date: 06-2020
Publisher: SAGE Publications
Date: 08-2001
Publisher: Cambridge University Press (CUP)
Date: 03-2022
DOI: 10.1017/NWS.2022.6
Abstract: 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 ERGM equivalents of structural effects as used in the SAOM. This turns the modeled endogeneity into circularity and obtained results are tautological. In consequence, their out-of-s le predictions using TERGMs are based on out-of-s le information and thereby predict the future using observations from the future. Thus, their analysis rests on erroneous model specifications that invalidate the article’s conclusions. Finally, beyond these specific points, we argue that their evaluation metric—tie-level predictive accuracy—is unsuited for the task of comparing model performance.
Publisher: Elsevier BV
Date: 11-2018
DOI: 10.1016/J.PUHE.2018.07.023
Abstract: 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. A mixed method study. Appropriate content was prepared through a literature review. Content validation indices were assessed using interviews with content experts and lay experts. A conservative approach was used to assess the inter-rater agreement among the participants about the instrument relevance and clarity. The scale content validity index was computed using the average method. Non-parametric Mokken scale analysis was used for assessing scalability and unidimensionality of the questionnaire in a s le of 170 FSWs in Tehran. To evaluate the reliability and internal consistency of the questionnaire intra-class correlation and Cronbach's alpha were employed. A list of 34 items was finalized, with subscales for actual behavioral norms and for perceived norms. The relevance of the actual and perceived norms subscales in the final questionnaire was higher than 96% clarity of the subtests was 99% and higher. The comprehensiveness of the actual and perceived norms subscales was 85% for both. Mokken scale analysis showed that the two subscales were distinct constructs, and all items are good indicators for the constructs. Our findings support that the safe sex norm questionnaire is a valid and reliable measure that would be useful to harm reduction programs and help effective HIV prevention among female sex workers.
Publisher: OpenEdition
Date: 03-1997
DOI: 10.4000/MSH.2744
Publisher: SAGE Publications
Date: 15-06-2010
DOI: 10.1111/J.1467-9531.2010.01225.X
Abstract: 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 underlying the observed dynamics, special diligence in data analysis is advisable. While a dependable and validmethod would benefit several research areas, according to the best of our knowledge, it has been lacking in the extant literature. In this paper, we present a recently developed family of statistical models that enables researchers to separate the two effects in a statistically adequate manner. To illustrate our method, we investigate the roles of homophile selection and peer influence mechanisms in the joint dynamics of friendship formation and substance use among adolescents. Making use of a three-wave panel measured in the years 1995–1997 at a school in Scotland, we are able to assess the strength of selection and influence mechanisms and quantify the relative contributions of homophile selection, assimilation to peers, and control mechanisms to observed similarity of substance use among friends.
Publisher: Elsevier BV
Date: 05-2007
Publisher: Cambridge University Press (CUP)
Date: 07-1999
DOI: 10.1017/S0144686X9900745X
Abstract: This longitudinal study aims to explain loneliness in newly bereaved older adults, taking into account personal and circumstantial conditions surrounding the partner's death. A distinction is made between emotional and social loneliness. Data were gathered both before and after partner loss. Results were interpreted within the framework of the Theory of Mental Incongruity. The findings reveal that being unable to anticipate the partner's death is related to higher levels of emotional loneliness. Standards of instrumental support, measured indirectly by poor physical condition, lead to stronger emotional as well as social loneliness. Standards measured directly by importance attached to support or contacts result in higher emotional loneliness but, unexpectedly, in lower social loneliness. Furthermore, difficulties with establishing personal contacts, caused, for instance, by social anxiety, add to loneliness. It is concluded that circumstances related to the partner's illness may contribute to emotional loneliness after bereavement. Moreover, the results highlight the importance of taking coping attitudes into consideration for a better understanding of how newly bereaved older adults adapt to the loss of a partner.
Publisher: American Meteorological Society
Date: 04-1986
Publisher: Wiley
Date: 24-01-2019
DOI: 10.1002/AB.21817
Publisher: Wiley
Date: 19-08-2013
DOI: 10.1111/JORA.12064
Publisher: Springer Science and Business Media LLC
Date: 05-11-2011
Publisher: Springer Science and Business Media LLC
Date: 1999
Publisher: Wiley
Date: 15-04-2020
DOI: 10.1111/STAN.12208
Publisher: Annual Reviews
Date: 07-03-2017
DOI: 10.1146/ANNUREV-STATISTICS-060116-054035
Abstract: 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 model for evolution of networks, attention is given to coevolution models. These use the same approach of a continuous-time Markov chain observed at a small number of time points, but now with an extended state space. The state space can be, for ex le, the combination of a network and nodal variables, or a combination of several networks. This leads to models for the dynamics of multivariate networks. The article emphasizes the approach to modeling and algorithmic issues for estimation some attention is given to comparison with other models.
Publisher: Elsevier BV
Date: 08-2021
DOI: 10.1016/J.SSRESEARCH.2021.102577
Abstract: This research focuses on ambivalence in family networks and presents a framework for investigating how triadic configurations, beyond specific dyads, may affect in idual outcomes such as well-being. First, the paper introduces the ambivalent triad census, counting the frequencies of 18 non-isomorphic triads in which ties can be positive, negative, or ambivalent, in non-directed networks, and proposes the linear combinations of three theoretical mechanisms (ambivalent balance, diffusion of stress, ide and conquer) predicting how embeddedness in an ambivalent triad may affect in idual well-being. Second, the ambivalent triad census is applied to 300 non-directed family networks, 150 stepfamilies and 150 first-time families, in which mothers reported about the relationships with and between family members. Results show that mothers embedded in triads exhibiting more ambivalent balance and less diffusion of stress score higher on social self-esteem. The study emphasizes the importance of studying ambivalence in higher-level relational structures, such as triads, in families.
Publisher: Springer International Publishing
Date: 2018
Publisher: JMIR Publications Inc.
Date: 19-12-2011
DOI: 10.2196/JMIR.1911
Publisher: SAGE Publications
Date: 08-2006
DOI: 10.1111/J.1467-9531.2006.00176.X
Abstract: The most promising class of statistical models for expressing structural properties of social networks observed at one moment in time is the class of exponential random graph models (ERGMs), also known as p* models. The strong point of these models is that they can represent a variety of structural tendencies, such as transitivity, that define complicated dependence patterns not easily modeled by more basic probability models. Recently, Markov chain Monte Carlo (MCMC) algorithms have been developed that produce approximate maximum likelihood estimators. Applying these models in their traditional specification to observed network data often has led to problems, however, which can be traced back to the fact that important parts of the parameter space correspond to nearly degenerate distributions, which may lead to convergence problems of estimation algorithms, and a poor fit to empirical data. This paper proposes new specifications of exponential random graph models. These specifications represent structural properties such as transitivity and heterogeneity of degrees by more complicated graph statistics than the traditional star and triangle counts. Three kinds of statistics are proposed: geometrically weighted degree distributions, alternating k-triangles, and alternating independent two-paths. Ex les are presented both of modeling graphs and digraphs, in which the new specifications lead to much better results than the earlier existing specifications of the ERGM. It is concluded that the new specifications increase the range and applicability of the ERGM as a tool for the statistical analysis of social networks.
Publisher: Wiley
Date: 10-04-2019
DOI: 10.1111/JORA.12501
Publisher: Universitat Autonoma de Barcelona
Date: 25-05-2002
DOI: 10.5565/REV/REDES.21
Publisher: Oxford University Press (OUP)
Date: 17-09-2008
DOI: 10.1007/S12160-008-9061-8
Abstract: 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 couples) in comparison to matched control couples (N = 64). Furthermore, the influence of neuroticism on distress was investigated. The Hospital Anxiety and Depression Scale was administered nine times over a 12-month period, and neuroticism was assessed at the beginning of the study using the Eysenck Personality Questionnaire. Multilevel analyses revealed that patients were more distressed during the first 15 months after diagnosis than nonpatients. A significant portion of the distress that could not be explained by the cancer experience was explained by neuroticism. Differences in distress between patients and comparison-control women are relatively small and decreased over time, while distress in male partners was not elevated in comparison to their controls.
Publisher: Springer Science and Business Media LLC
Date: 15-07-2019
DOI: 10.1007/S11336-019-09676-3
Abstract: 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 natural way to the parameters. Here, we propose to apply the generalized method of moments (GMoM), using more statistics than parameters. We concentrate on statistics depending jointly on the network and the behaviour, because of the importance of their interdependence, and propose to add contemporaneous statistics to the usual cross-lagged statistics. We describe the stochastic algorithm developed to approximate the GMoM solution. A small simulation study supports the greater statistical efficiency of the GMoM estimator compared to the MoM.
Publisher: Elsevier BV
Date: 05-2017
Publisher: Springer Science and Business Media LLC
Date: 02-09-2021
Publisher: Wiley
Date: 12-1999
Publisher: Springer Science and Business Media LLC
Date: 06-12-2021
DOI: 10.1186/S12889-021-12266-7
Abstract: 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 in idual characteristics of the FSWs and of their sexual partners, characteristics of their relationship, and the FSW’s personal network. A cross-sectional ego-centric network survey of 170 FSWs was carried out in Tehran between January and June 2017. A multilevel ordered logistic regression analysis was conducted to examine the effects of in idual and relational characteristics simultaneously. Condom use in sexual relationships of the FSWs on average was rather low. Important determinants of safe sexual behavior were found both at the level of the in idual FSW and at the level of the sexual partner. The main determinants at the level of the in idual FSW were FSWs’ age and HIV knowledge. At the level of the sexual partner, age and education of sexual partners, as well as intimacy, duration of tie, frequency of contacts with a given partner, frequency of contact, perceived social support, and perceived safe sex norms were significantly associated with condom use. The findings highlighted that considering only the in idual characteristics of female sex workers is not sufficient for effectively promoting condom use. Factors at the network and dyadic level should also be considered, especially the role of sexual partners. Network-based interventions may be useful which modify social relationships to create a social environment that can facilitate changes in sexual behavior.
Publisher: Emerald (MCB UP )
Date: 2006
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 2009
DOI: 10.1097/GME.0B013E31817FA9E0
Abstract: To evaluate the effectiveness of a phytotherapeutic intervention comprising a combination of Hypericum perforatum (St. John's wort) and Vitex agnus-castus (Chaste tree/berry) in the management of menopausal symptoms. A double-blind, randomized, placebo-controlled, parallel trial was performed over 16 weeks in 100 eligible late-perimenopausal or postmenopausal women experiencing hot flushes and other menopausal symptoms. Herbal combination therapy or placebo tablets were administered twice daily. The primary endpoint was hot flush episodes. Secondary endpoints included Greene Climacteric Scale scores, Hamilton Depression Inventory scores, and Utian Quality of Life Scale scores. Ninety-three women completed the study. Data analysis on an intent-to-treat basis found no significant differences between the two groups for any of the endpoints. Analyses performed at interim data time points revealed no significant differences at week 4, 8, or 12 for daily weighted flushes or scores on the Greene Climacteric Scale or Hamilton Depression Inventory. However, significant improvements across the treatment phase were observed in both the placebo and active treatment groups for these endpoints. No significant change was found for either group on quality of life. The herbal combination of H. perforatum and V. agnus-castus was not found to be superior to placebo for the treatment of menopausal symptoms. The herbal combination was well tolerated with no significant adverse events noted in the short term. Robust findings from quality studies such as this are important for informing the community, healthcare providers, and regulatory authorities.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Tom Snijders.