Assessing and accounting for time heterogeneity in stochastic actor oriented models

Dynamic social network analysis of a brief alcohol intervention trial in heavy-drinking college students shows spillover effects

BACKGROUND

Heavy-drinking college students tend to have close social networks, and there is theoretical and empirical support for the idea that behavior change can spread through those networks via close ties. The objective of this research was to determine whether intervention-induced behavior change in a subset of heavy drinkers in a sociometric (whole) college class-year social network is transmitted to other heavy drinkers in the network, resulting in reduced behavioral risk and change in network ties.

METHODS

We conducted a controlled trial in which most of a first-year college class (N = 1236; 56.9% female) was enrolled, with alcohol use and social network ties measured early in each of three semesters. Following a baseline assessment, the network was divided into two groups, brief motivational intervention (BMI) and natural history control (NHC) according to dormitory residence location. A subset of heavy drinkers in each group was selected, and those in the BMI group received an in-person intervention.

RESULTS

Using stochastic actor-oriented modeling, we found a significant tendency for participants in the BMI group to shed ties with individuals with similar drinking behaviors between the first and second semesters, relative to the NHC group. Furthermore, heavy drinkers with reciprocal ties to intervention recipients in the BMI group showed a significant reduction in drinks per week.

CONCLUSIONS

Individual alcohol interventions appear to have effects both on behavior and network connections among individuals who did not receive the intervention. Continued research is needed to identify the optimal conditions for the diffusion of behavior change.

A tutorial for modeling the evolution of network dynamics for multiple groups

Researchers have been increasingly taking advantage of the stochastic actor-oriented modeling framework as a method to analyze the evolution of network ties. Although the framework has proven to be a useful method to model longitudinal network data, it is designed to analyze a sample of one bounded network. For group and team researchers, this can be a significant limitation because such researchers often collect data on more than one team. This paper presents a nontechnical and hands-on introduction for a meta-level technique for stochastic actor-oriented models in RSIENA where researchers can simultaneously analyze network drivers from multiple samples of teams and groups. Moreover, we follow up with a multilevel Bayesian version of the model when it is appropriate. We also provide a framework for researchers to understand what types of research questions and theories could be examined and tested.

Relationships between changing communication networks and changing perceptions of psychological safety in a team science setting: Analysis with actor-oriented social network models

A growing evidence base suggests that complex healthcare problems are optimally tackled through cross-disciplinary collaboration that draws upon the expertise of diverse researchers. Yet, the influences and processes underlying effective teamwork among independent researchers are not well-understood, making it difficult to fully optimize the collaborative process. To address this gap in knowledge, we used the annual NIH mHealth Training Institutes as a testbed to develop stochastic actor-oriented models that explore the communicative interactions and psychological changes of its disciplinarily and geographically diverse participants. The models help investigate social influence and social selection effects to understand whether and how social network interactions influence perceptions of team psychological safety during the institute and how they may sway communications between participants. We found a degree of social selection effects: in particular years, scholars were likely to choose to communicate with those who had more dissimilar levels of psychological safety. We found evidence of social influence, in particular, from scholars with lower psychological safety levels and from scholars with reciprocated communications, although the sizes and directions of the social influences somewhat varied across years. The current study demonstrated the utility of stochastic actor-oriented models in understanding the team science process which can inform team science initiatives. The study results can contribute to theory-building about team science which acknowledges the importance of social influence and selection.

Uncovering the Effect of Forest Certification on the Dynamic Evolution of the Global Log Trade Network: A Stochastic Actor-Oriented Model Approach

Clarifying the dynamic evolution characteristics and driving mechanism of the global log trade network (GLTN) can provide references for the trade decision-making of various countries. Based on the stochastic actor-oriented model, this paper analyzed the GLTN’s dynamic evolution from 2010 to 2019 and paid more attention to the effect of forest certification on the dynamic evolution of the GLTN. Results indicate that from 2010 to 2019, many changes have occurred in the network. The change rate in the 2010–2015 period is faster than that in the 2015–2019 period. Countries tend to form reciprocity, three-cycles, and transitive trade ties over time. A country with more certified forest area tends to form new log export ties with the other countries. The trade imbalance ratio (TII) has a significant negative mediating effect on the evolutionary relationships between the certified forest area and the log trade network dynamic. Net exporters of log tend to avoid establishing export ties with countries with more certified forest areas over time. Countries with similar cultural backgrounds are easier to establish log trade ties with, while countries with farther geographical distances tend to avoid establishing trade ties over time. A free trade agreement (FTA) has a significant positive impact on the formation of log trade ties among nations. Our findings shed new light on the dynamic evolution mechanism of the global log trade network and offer implications for future trade and forest conservation policy design.

Effects of social networks on interventions to change conservation behavior

Social networks are critical to the success of behavioral interventions in conservation because network processes such as information flows and social influence can enable behavior change to spread beyond a targeted group. We investigated these mechanisms in the context of a social marketing campaign to promote a wildlife poisoning hotline in Cambodia. With questionnaire surveys we measured a social network and knowledge and constructs from the theory of planned behavior at 3 points over 6 months. The intervention initially targeted ∼11% (of 365) of the village, but after 6 months ∼40% of the population was knowledgeable about the campaign. The likelihood of being knowledgeable nearly doubled with each additional knowledgeable household member. In the short term, there was also a modest, but widespread improvement in proconservation behavioral intentions, but this did not persist after 6 months. Estimates from stochastic actor-oriented models suggested that the influences of social peers, rather than knowledge, were driving changes in intention and contributed to the failure to change behavioral intention in the long term, despite lasting changes in attitudes and perceived norms. Our results point to the importance of accounting for the interaction between networks and behavior when designing conservation interventions.

Assessing Peer Influence and Susceptibility to Peer Influence Using Individual and Dyadic Moderators in a Social Network Context: The Case of Adolescent Alcohol Misuse

Higher accepted friends are known to influence the alcohol misuse of lower accepted friends, but not the reverse. The present study was designed to address the origins of this influence: Are higher accepted friends particularly influential or are lower accepted friends particularly susceptible to influence? To address this question, we introduce an innovative application of longitudinal social network techniques (RSIENA) designed to distinguish being influential from being susceptible to influence. The results revealed that influence was a product of heightened susceptibility among low accepted adolescents, rather than heightened influence among high accepted adolescents. The findings are consistent with claims that low accepted youth fear the consequences of nonconformity and adjust their behavior to more closely resemble their affiliates.

The Role of Cognitive Emotion Regulation for Making and Keeping Friend and Conflict Networks

We used social network analysis (SNA) to examine how adaptive ER strategies (acceptance, positive reappraisal, refocusing, and putting in perspective) and maladaptive ER strategies (rumination, catastrophizing, self- and other-blame) predict the creation and maintenance of friendship and conflict relationships within a mixed-gender social group. Participants (n = 193, 53% female, M age = 19.4 years, 62.1% White) reported on emotion regulation, friendship, and conflict nominations at two time points. Stochastic actor-oriented models revealed that similarity in endorsement of adaptive ER strategies predicted maintenance of friendship and conflict relationships over time. However, new conflict relationships were more likely to form between those who differed in use of adaptive ER. Finally, more frequent use of maladaptive ER strategies was related to termination of existing conflict ties and the creation of new ones. Deploying social network analysis as a methodology for examining social relationships enables the unpacking the dynamics of multiple social relationships (friend and conflict), identifying the role of ER for structuring of social relationships among group members. Although cognitive ER is an intra-individual process, it fundamentally occurs within a social environment and our results advance the knowledge of how ER contributes to how this social environment is created in a first place.

Political Alliance Formation and Cooperation Networks in the Utah State Legislature

Social network analysis has become an increasingly important tool among political scientists for understanding legislative cooperation in modern, democratic nation-states. Recent research has demonstrated the influence that group affinity (homophily) and mutual exchanges (reciprocity) have in structuring political relationships. However, this literature has typically focused on political cooperation where costs are low, relationships are not exclusive, and/or partisan competition is high. Patterns of legislative behavior in alternative contexts are less clear and remain largely unexamined. Here, we compare theoretical expectations of cooperation in these contexts from the political and biosocial sciences and implement the first assessment of political alliance formation in a novel legislative environment where costs to cooperation are high and party salience low. We implement a stochastic actor-oriented model (SAOM) to examine bill floor sponsorship, a process in which a "floor sponsor" becomes the exclusive advocate for a colleague's piece of legislation, in the Utah state legislature from 2005 to 2008-a context in which gender (male) and political party (Republican) supermajorities exist. We find that (1) party and gender homophily predict who legislators recruit as floor sponsors, whereas seniority does not, and (2) legislators frequently engage in reciprocal exchanges of floor sponsorship. In addition, whereas gender homophily increases the likelihood of reciprocity, party homophily decreases it. Our findings suggest that when the cost of cooperation is high, political actors use in-group characteristics for initiating alliances, but once a cooperative relationship is established with an out-group political member, it is reinforced through repeated exchanges. These findings may be useful for understanding the rise of political polarization and gridlock in democracies internationally.

Contagious Health Risk and Precautionary Social Distancing

Background

Since humans are social animals, social relations are incredibly important. However, in cases of contagious diseases such as the flu, social contacts also pose a health risk. According to prominent health behavior change theories, perceiving a risk for one’s health motivates precautionary behaviors. The “behavioral immune system” approach suggests that social distancing might be triggered as a precautionary, evolutionarily learned behavior to prevent transmitting contagious diseases through social contact. This study examines the link between personal risk perception for an infectious disease and precautionary behavior for disease-prevention in the context of social relationships.

Methods

At 2-week intervals during the first semester, 100 Psychology freshmen indicated their flu risk perception, whether they had been ill during the previous week, and their friendships within their freshmen network for eight time points.

Results

Social network analysis revealed that participants who reported a high flu risk perception listed fewer friends (B = −0.10, OR = 0.91, p = 0.026), and were more likely to be ill at the next measuring point (B = 0.26, OR = 1.30, p = 0.005). Incoming friendship nominations increased the likelihood of illness (B = 0.14, OR = 1.15, p = 0.008), while the reduced number of friendship nominations only marginally decreased this likelihood (B = −0.07, OR = 0.93, p = 0.052).

Conclusion

In accordance with the concept of a “behavioral immune system,” participants with high flu risk perception displayed a social precautionary distancing even when in an environment, in which the behavior was ineffective to prevent an illness.

Coalitions and conflict: A longitudinal analysis of men's politics

To negotiate conflict and navigate status hierarchy, individuals in many species form coalitions. We describe inter-personal conflicts and assess theories of coalition formation in a small-scale human society. Based on longitudinal and cross-sectional social network analysis of men in two communities of Tsimane forager-horticulturalists, we find evidence of reciprocity in coalitional support, as well as evidence of transitivity: an ally of my ally is likely to become my ally. We find mixed support for coalition formation between individuals who share a common adversary. Coalition formation was also predicted by food- and labour-sharing and especially by kinship. Physically formidable men and men higher in informal status were more likely to provide coalitional support over time; evidence was mixed that they receive more coalitional support. The highest status men are hubs of a dense coalitional support network that indirectly link all men in the community. These findings suggest that male coalition formation is multiply motivated, and in general reveals the political dynamics that structure men's lives in small, relatively egalitarian communities.

Understanding Allogrooming Through a Dynamic Social Network Approach: An Example in a Group of Dairy Cows

For gregarious species such as domestic cattle, the social environment is a very important determinant of their welfare and fitness. Understanding the complexity of cows' relationships can assist the development of management practices that are more integrated with the cows' social behavioral processes. The two aims of this study were: (1) to determine the dynamics of affiliative relationships, as indicated by allogrooming, by means of stochastic actor-oriented modeling, in dairy cows during early lactation; (2) to explore the underlying processes and the individual attributes, such as age, social rank and reproductive state, that could shape network pattern changes in grooming contacts between individual. We observed the allogrooming behavior of a dynamic group of 38 dairy cows for 4 h per day for 30 days. Using stochastic actor-oriented models, we modeled the dynamics of weekly contacts and studied how structural processes (e.g., reciprocity, transitivity, or popularity) and individual attributes (i.e., age, social rank, and reproductive state) influence network changes. We found that cows tended to groom individuals that had previously groomed them, implying a possible cooperation. Cows that groomed more actively did not appear to have a preference for specific individuals in the herd, and in return, tended to be groomed by fewer cows over time. Older individuals groomed more cows than younger ones, indicating that allogrooming could be related to seniority. Cows groomed mainly individuals of similar age, suggesting that familiarity and growing up together enhanced social grooming. Over time, cows with higher social rank were groomed by fewer cows and individuals recently reintroduced to the group groomed more herdmates. The study of social network dynamics can be used to better understand the complexity and non-linearity of cow relationships. Our findings, along with further research, can complement and strengthen the design of improved management practices that are more in line with the natural social behavior of cows.

Dynamic pathways between rejection and antisocial behavior in peer networks: Update and test of confluence model

The confluence model theorizes that dynamic transactions between peer rejection and deviant peer clustering amplify antisocial behavior (AB) within the school context during adolescence. Little is known about the links between peer rejection and AB as embedded in changing networks. Using longitudinal social network analysis, we investigated the interplay between rejection, deviant peer clustering, and AB in an ethnically diverse sample of students attending public middle schools (N = 997; 52.7% boys). Adolescents completed peer nomination reports of rejection and antisocial behavior in Grades 6-8. Results revealed that rejection status was associated with friendship selection, and adolescents became rejected if they were friends with others who were rejected. Youth befriended others with similar levels of AB. Significant patterns of peer influence were documented for AB and rejection. As hypothesized, rejected youth with low AB were more likely to affiliate with others with high AB instead of similarly low AB. In contrast, nonrejected youth preferred to befriend others with similarly high or low AB. Results support an updated confluence model of a joint interplay between rejection and AB as ecological conditions that lead to self-organization into deviant clusters in which peer contagion on problem behaviors operates.

Goodness of fit for stochastic actor-oriented models

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.

Smoking Diffusion through Networks of Diverse, Urban American Adolescents over the High School Period

This study uses recent data to investigate if smoking initiation diffuses through friendship networks over the high school period and explores if diffusion processes differ across schools. One thousand four hundred and twenty-five racially and ethnically diverse youth from four high schools in Los Angeles were surveyed four times over the high school period from 2010 to 2013. Probit regression models and stochastic actor-based models for network dynamics tested for peer effects on smoking initiation. Friend smoking was found to predict adolescent smoking, and smoking initiation diffused through friendship networks in some but not all of the schools. School differences in smoking rates and the popularity of smokers may be linked to differences in the diffusion of smoking through peer networks. We conclude that there are differences in peer effects on smoking initiation across schools that will be important to account for in network-based smoking interventions.

The dynamics of men's cooperation and social status in a small-scale society

We propose that networks of cooperation and allocation of social status co-emerge in human groups. We substantiate this hypothesis with one of the first longitudinal studies of cooperation in a preindustrial society, spanning 8 years. Using longitudinal social network analysis of cooperation among men, we find large effects of kinship, reciprocity and transitivity in the nomination of cooperation partners over time. Independent of these effects, we show that (i) higher-status individuals gain more cooperation partners, and (ii) individuals gain status by cooperating with individuals of higher status than themselves. We posit that human hierarchies are more egalitarian relative to other primates species, owing in part to greater interdependence between cooperation and status hierarchy.

The Co-evolution of Bullying Perpetration, Homophobic Teasing, and a School Friendship Network

Bullying and homophobic teasing behaviors affect the lives of many school aged children, often co-occur, and tend to peak in middle school. While bullying and homophobic teasing behaviors are known to be peer group phenomena, studies typically examine the associations at the individual or school levels. An examination of these behaviors at the peer group level can aid in our understanding of the formation and maintenance of peer groups that engage in these forms of aggressive behavior (selection), and the extent to which friends and the peer group impact individual rates of these aggressive behaviors (influence). In this longitudinal study, we assess the co-evolution of friendship networks, bullying perpetration, and homophobic teasing among middle school students (n = 190) using a Stochastic Actor-Based Model (SABM) for longitudinal networks. Data were collected from 6-8th-grade students (Baseline age 12-15; 53% Female; 47% Male) across three waves of data. The sample was diverse with 58% African American, 31% White, and 11% Hispanic. Since bullying and homophobic teasing behaviors are related yet distinct forms of peer aggression, to capture the unique and combined effects of these behaviors we ran models separately and then together in a competing model. Results indicated that on average individuals with higher rates of bullying perpetration and homophobic teasing were associated with becoming increasingly popular as a friend. However, the effects were not linear, and individuals with the highest rates of bullying perpetration and homophobic teasing were less likely to receive friendship nominations. There was no evidence that bullying perpetration or homophobic teasing were associated with the number of friendship nominations made. Further, there was a preference for individuals to form or maintain friendships with peers who engaged in similar rates of homophobic name-calling; however, this effect was not found for bullying perpetration. Additionally, changes in individual rates of bullying perpetration were not found to be predicted by the bullying perpetration of their friends; however, changes in adolescent homophobic teasing were predicted by the homophobic teasing behaviors of their friends. In a competing model that combined bullying perpetration and homophobic teasing, we found no evidence that these behaviors were associated with popularity. These findings are likely due to the high association between bullying perpetration and homophobic teasing combined with the small sample size. However, friendship selection was based on homophobic name-calling, such that, there was a preference to befriend individuals with similar rates of homophobic teasing. We also examined several risk factors (dominance, traditional masculinity, impulsivity, femininity, positive attitudes of bullying, and neighborhood violence), although, impulsivity was the only covariate that was associated with higher levels of bullying perpetration and homophobic teasing. More specifically, youth with higher rates of impulsivity engaged in higher rates of bullying perpetration and homophobic teasing over time. The findings suggest bullying perpetration and homophobic teasing have important influences on friendship formation, and close friendships influence youth's engagement in homophobic teasing. Implications for prevention and intervention efforts are discussed in terms of targeting peer groups and popular peers to help reduce rates of these aggressive behaviors.

Analytic Strategies for Longitudinal Networks with Missing Data

Missing data are often problematic when analyzing complete longitudinal social network data. We review approaches for accommodating missing data when analyzing longitudinal network data with stochastic actor-based models. One common practice is to restrict analyses to participants observed at most or all time points, to achieve model convergence. We propose and evaluate an alternative, more inclusive approach to sub-setting and analyzing longitudinal network data, using data from a school friendship network observed at four waves (N =694). Compared to standard practices, our approach retained more information from partially observed participants, generated a more representative analytic sample, and led to less biased model estimates for this case study. The implications and potential applications for longitudinal network analysis are discussed.

Peer Influence on Ethnic-Racial Identity Development: A Multi-Site Investigation

The peer context features prominently in theory, and increasingly in empirical research, about ethnic-racial identity (ERI) development, but no studies have assessed peer influence on ERI using methods designed to properly assess peer influence. We examined peer influence on ERI centrality, private, and public regard using longitudinal social network analysis. Data were drawn from two sites: a predominantly Latina/o Southwestern (SW) school (N = 1034; Mage = 12.10) and a diverse Midwestern (MW) school (N = 513; Mage = 11.99). Findings showed that peers influenced each other's public regard over time at both sites. However, peer influence on centrality was evident in the SW site, whereas peer influence on private regard was evident in the MW site. Importantly, peer influence was evident after controlling for selection effects. Our integration of developmental, contextual, and social network perspectives offers a fruitful approach to explicate how ERI content may shift in early adolescence as a function of peer influence.

Co-evolution of Friendships and Antipathies: A Longitudinal Study of Preschool Peer Groups

We used stochastic actor-based models to test whether the developmental dynamics of friendships and antipathies in preschool peer groups (followed throughout three school years) were co-dependent. We combined choices from three sociometric tasks of 142 children to identify friendship and antipathy ties and used SIENA to model network dynamics. Our results show that different social processes drive the development of friendship and antipathy ties, and that they do not develop in association (i.e., friendship ties are not dependent on existing antipathies, and vice-versa). These results differ from those of older children (age range = 10-14) suggesting that the interplay of friendship and antipathy only plays a significant role in the peer group context in older children. We propose these differences to be likely related with preschool age children's inaccurate perceptions of their classmates' relationships, particularly of their antipathies, and/or with the absence of shared norms to deal with antipathetic relationships.

Social Networks and the Diffusion of Adolescent Problem Behavior: Reliable Estimates of Selection and Influence from Sixth Through Ninth Grades

Seeking to reduce problematic peer influence is a prominent theme of programs to prevent adolescent problem behavior. To support the refinement of this aspect of prevention programming, we examined peer influence and selection processes for three problem behaviors (delinquency, alcohol use, and smoking). We assessed not only the overall strengths of these peer processes, but also their consistency versus variability across settings. We used dynamic stochastic actor-based models to analyze five waves of friendship network data across sixth through ninth grades for a large sample of U.S. adolescents. Our sample included two successive grade cohorts of youth in 26 school districts participating in the PROSPER study, yielding 51 longitudinal social networks based on respondents' friendship nominations. For all three self-reported antisocial behaviors, we found evidence of both peer influence and selection processes tied to antisocial behavior. There was little reliable variance in these processes across the networks, suggesting that the statistical imprecision of the peer influence and selection estimates in previous studies likely accounts for inconsistencies in results. Adolescent friendship networks play a strong role in shaping problem behavior, but problem behaviors also inform friendship choices. In addition to preferring friends with similar levels of problem behavior, adolescents tend to choose friends who engage in problem behaviors, thus creating broader diffusion.

A Mathematical Framework for the Complex System Approach to Group Dynamics: The Case of Recovery House Social Integration

The complex system conception of group social dynamics often involves not only changing individual characteristics, but also changing within-group relationships. Recent advances in stochastic dynamic network modeling allow these interdependencies to be modeled from data. This methodology is discussed within a context of other mathematical and statistical approaches that have been or could be applied to study the temporal evolution of relationships and behaviors within small- to medium-sized groups. An example model is presented, based on a pilot study of five Oxford House recovery homes, sober living environments for individuals following release from acute substance abuse treatment. This model demonstrates how dynamic network modeling can be applied to such systems, examines and discusses several options for pooling, and shows how results are interpreted in line with complex system concepts. Results suggest that this approach (a) is a credible modeling framework for studying group dynamics even with limited data, (b) improves upon the most common alternatives, and (c) is especially well-suited to complex system conceptions. Continuing improvements in stochastic models and associated software may finally lead to mainstream use of these techniques for the study of group dynamics, a shift already occurring in related fields of behavioral science.

The importance of perceived care and connectedness with friends and parents for adolescent social anxiety

Nonclinical social anxiety in adolescence can be highly problematic, as it likely affects current and especially new social interactions. Relationships with significant others, such as close friends, mothers, and fathers, could aid socially anxious adolescents' participation in social situations, thereby helping reduce feelings of social anxiety. We examined whether making friends as well as high friendship quality help reduce social anxiety over time, and whether friends', mothers', and fathers' care interact in reducing social anxiety. Using longitudinal data from 2,194 participants in a social network (48% girls; Mage  = 13.58) followed for 3 years, we estimated friendship selection and influence processes via a continuous time-modeling approach using SIENA. We controlled for the effects of depressive symptoms, self-esteem, gender, age, and family structure. Our findings suggest that perceived care by friends mediated the effect of making friends on social anxiety. Perceptions of mother and father, as well as friend care and connectedness, respectively, did not interact in decreasing social anxiety. Nonetheless, care and connectedness with mothers, fathers, and friends jointly predicted decreases in social anxiety. Caring relationships with friends and parents each play a role in mutually protecting early adolescents against increasing in social anxiety over time.

Influences between Online–Exclusive, Conjoint and Offline–Exclusive Friendship Networks: The Moderating Role of Shyness

Prior research has indicated that shy adolescents are more motivated to form friendships online than to form friendships offline. Little is known about whether having friendships found exclusively online may impact self–esteem and forming offline friendships for these adolescents. This study therefore aimed to provide insight into the moderating role of shyness in the longitudinal interplay between friendships in online and offline contexts in early adolescence. Adolescents and their friends (193 girls, 196 boys; Mage = 13.29) were followed with three consecutive measurements with intervals of eight months. Results showed that particularly for shy adolescents, having friends exclusively online predicted increases in self–esteem. Self–esteem, in turn, was found to predict forming more friendships found both offline and online and forming more friendships found exclusively offline. Thus, findings supported the social compensation perspective that shy adolescents may benefit from having friends exclusively online, as these friendships may increase self–esteem, thereby facilitating the formation of friendships found partially and completely offline. Copyright © 2013 John Wiley & Sons, Ltd.

Onset to First Alcohol Use in Early Adolescence: A Network Diffusion Model

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 use. Meta-analysis of individual models for 12 schools found significant effects for friendship selection based on the same alcohol use status, and for an increased rate of onset to first use based on exposure to already-onset peers. Onset rate was greater at higher grades and among participants who spent more unsupervised time with friends. Neither selection nor exposure effects interacted with grade, adult supervision, or gender.

Direct and Indirect Peer Socialization of Adolescent Nonsuicidal Self-Injury

This study examined direct and indirect forms of peer socialization of non-suicidal self-injury (NSSI) in adolescent friendship networks. Data were collected among 348 adolescents (55% females; Mage = 15.02 years; SD = 0.53) at 4 assessment waves. Stochastic actor-based models revealed no evidence for direct socialization of NSSI: adolescents whose friends reported higher NSSI did not increase their NSSI over time. However, indirect forms of socialization were found. After controlling for direct socialization and selection effects, friends' depressive symptoms predicted changes in male and female adolescents' NSSI and friends' impulsivity predicted changes in male adolescents' NSSI. Findings highlight the importance of extending peer influence research beyond the classical "modeling" paradigm by providing evidence that peers may indirectly socialize adolescents' NSSI.

Statistical modelling of network panel data: goodness of fit

Networks of relationships between individuals influence individual and collective outcomes and are therefore of interest in social psychology, sociology, the health sciences, and other fields. We consider network panel data, a common form of longitudinal network data. In the framework of estimating functions, which includes the method of moments as well as the method of maximum likelihood, we propose score-type tests. The score-type tests share with other score-type tests, including the classic goodness-of-fit test of Pearson, the property that the score-type tests are based on comparing the observed value of a function of the data to values predicted by a model. The score-type tests are most useful in forward model selection and as tests of homogeneity assumptions, and possess substantial computational advantages. We derive one-step estimators which are useful as starting values of parameters in forward model selection and therefore complement the usefulness of the score-type tests. The finite-sample behaviour of the score-type tests is studied by Monte Carlo simulation and compared to t-type tests.