Priority populations' experiences of isolation, quarantine and distancing for COVID-19: protocol for a longitudinal cohort study (Optimise Study).

Introduction: Longitudinal studies can provide timely and accurate information to evaluate and inform COVID-19 control and mitigation strategies and future pandemic preparedness. The Optimise Study is a multidisciplinary research platform established in the Australian state of Victoria in September 2020 to collect epidemiological, social, psychological and behavioural data from priority populations. It aims to understand changing public attitudes, behaviours and experiences of COVID-19 and inform epidemic modelling and support responsive government policy.

Multilevel network interventions: Goals, actions, and outcomes.

COVID-19 has resulted in dramatic and widespread social network interventions across the globe, with public health measures such as distancing and isolation key epidemiological responses to minimize transmission. Because these measures affect social interactions between people, the networked structure of daily lives is changed. Such largescale changes to social structures, present simultaneously across many different societies and touching many different people, give renewed significance to the conceptualization of social network interventions.

Exponential random graph model parameter estimation for very large directed networks.

Exponential random graph models (ERGMs) are widely used for modeling social networks observed at one point in time. However the computational difficulty of ERGM parameter estimation has limited the practical application of this class of models to relatively small networks, up to a few thousand nodes at most, with usually only a few hundred nodes or fewer. In the case of undirected networks, snowball sampling can be used to find ERGM parameter estimates of larger networks via network samples, and recently published improvements in ERGM network distribution sampling and ERGM estimation algorithms have allowed ERGM parameter estimates of undirected networks with over one hundred thousand nodes to be made.

Norm talk and human cooperation: Can we talk ourselves into cooperation?

Norm talk is verbal communication that explicitly states or implicitly implies a social norm. To investigate its ability to shape cultural dynamics, 2 types of norm talk were examined: injunction, which explicitly states what should be done, and gossip, which implies a norm by stating an action approved or disapproved of by the communicator. In 2 experiments, participants engaged in norm talk in repeated public goods games.

Outliers and Influential Observations in Exponential Random Graph Models.

We discuss measuring and detecting influential observations and outliers in the context of exponential family random graph (ERG) models for social networks. We focus on the level of the nodes of the network and consider those nodes whose removal would result in changes to the model as extreme or "central" with respect to the structural features that "matter". We construe removal in terms of two case-deletion strategies: the tie-variables of an actor are assumed to be unobserved, or the node is removed resulting in the induced subgraph.

Fast Maximum Likelihood Estimation via Equilibrium Expectation for Large Network Data.

A major line of contemporary research on complex networks is based on the development of statistical models that specify the local motifs associated with macro-structural properties observed in actual networks. This statistical approach becomes increasingly problematic as network size increases. In the context of current research on efficient estimation of models for large network data sets, we propose a fast algorithm for maximum likelihood estimation (MLE) that affords a significant increase in the size of networks amenable to direct empirical analysis.

Diversity and Community Can Coexist.

We examine the (in)compatibility of diversity and sense of community by means of agent-based models based on the well-known Schelling model of residential segregation and Axelrod model of cultural dissemination. We find that diversity and highly clustered social networks, on the assumptions of social tie formation based on spatial proximity and homophily, are incompatible when agent features are immutable, and this holds even for multiple independent features. We include both mutable and immutable features into a model that integrates Schelling and Axelrod models, and we find that even for multiple independent features, diversity and highly clustered social networks can be incompatible on the assumptions of social tie formation based on spatial proximity and homophily.

A Simulation Study Comparing Epidemic Dynamics on Exponential Random Graph and Edge-Triangle Configuration Type Contact Network Models.

We compare two broad types of empirically grounded random network models in terms of their abilities to capture both network features and simulated Susceptible-Infected-Recovered (SIR) epidemic dynamics. The types of network models are exponential random graph models (ERGMs) and extensions of the configuration model. We use three kinds of empirical contact networks, chosen to provide both variety and realistic patterns of human contact: a highly clustered network, a bipartite network and a snowball sampled network of a "hidden population".

Social encounter profiles of greater Melbourne residents, by location--a telephone survey.

Background: Models of infectious disease increasingly seek to incorporate heterogeneity of social interactions to more accurately characterise disease spread. We measured attributes of social encounters in two areas of Greater Melbourne, using a telephone survey.

Methods: A market research company conducted computer assisted telephone interviews (CATIs) of residents of the Boroondara and Hume local government areas (LGAs), which differ markedly in ethnic composition, age distribution and household socioeconomic status.

Hepatitis C transmission and treatment as prevention - The role of the injecting network.

Background: The hepatitis C virus (HCV) epidemic is a major health issue; in most developed countries it is driven by people who inject drugs (PWID). Injecting networks powerfully influence HCV transmission. In this paper we provide an overview of 10 years of research into injecting networks and HCV, culminating in a network-based approach to provision of direct-acting antiviral therapy.

The impact of injecting networks on hepatitis C transmission and treatment in people who inject drugs.

Unlabelled: With the development of new highly efficacious direct-acting antiviral (DAA) treatments for hepatitis C virus (HCV), the concept of treatment as prevention is gaining credence. To date, the majority of mathematical models assume perfect mixing, with injectors having equal contact with all other injectors. This article explores how using a networks-based approach to treat people who inject drugs (PWID) with DAAs affects HCV prevalence.

Ultrametric distribution of culture vectors in an extended Axelrod model of cultural dissemination.

The Axelrod model of cultural diffusion is an apparently simple model that is capable of complex behaviour. A recent work used a real-world dataset of opinions as initial conditions, demonstrating the effects of the ultrametric distribution of empirical opinion vectors in promoting cultural diversity in the model. Here we quantify the degree of ultrametricity of the initial culture vectors and investigate the effect of varying degrees of ultrametricity on the absorbing state of both a simple and extended model.

Hepatitis C transmission and treatment in contact networks of people who inject drugs.

Hepatitis C virus (HCV) chronically infects over 180 million people worldwide, with over 350,000 estimated deaths attributed yearly to HCV-related liver diseases. It disproportionally affects people who inject drugs (PWID). Currently there is no preventative vaccine and interventions feature long treatment durations with severe side-effects.

Hepatitis C virus phylogenetic clustering is associated with the social-injecting network in a cohort of people who inject drugs.

It is hypothesized that social networks facilitate transmission of the hepatitis C virus (HCV). We tested for association between HCV phylogeny and reported injecting relationships using longitudinal data from a social network design study. People who inject drugs were recruited from street drug markets in Melbourne, Australia.

Influence of contact definitions in assessment of the relative importance of social settings in disease transmission risk.

Background: Realistic models of disease transmission incorporating complex population heterogeneities require input from quantitative population mixing studies. We use contact diaries to assess the relative importance of social settings in respiratory pathogen spread using three measures of person contact hours (PCH) as proxies for transmission risk with an aim to inform bipartite network models of respiratory pathogen transmission.

Methods And Findings: Our survey examines the contact behaviour for a convenience sample of 65 adults, with each encounter classified as occurring in a work, retail, home, social, travel or "other" setting.

Homophily and contagion as explanations for weight similarities among adolescent friends.

Purpose: To determine whether weight-based similarities among adolescent friends result from social influence processes, after controlling for the role of weight on friendship selection and other confounding influences.

Methods: Four waves of data were collected from a grade 8 cohort of adolescents (N = 156, mean age = 13.6 years) over their initial 2 years of high school.

How physical activity shapes, and is shaped by, adolescent friendships.

The current study explored the role of school-based friendship networks in adolescents' engagement in physical activity (PA). It was hypothesized that similar participation in PA would be a basis for friendship formation, and that friends would also influence behavior. Whether these processes were mediated through cognitive mechanisms was also explored.

Comparison of three methods for ascertainment of contact information relevant to respiratory pathogen transmission in encounter networks.

Background: Mathematical models of infection that consider targeted interventions are exquisitely dependent on the assumed mixing patterns of the population. We report on a pilot study designed to assess three different methods (one retrospective, two prospective) for obtaining contact data relevant to the determination of these mixing patterns.

Methods: 65 adults were asked to record their social encounters in each location visited during 6 study days using a novel method whereby a change in physical location of the study participant triggered data entry.

Ceremonies of the whole: does social participation moderate the mood consequences of neuroticism?

Background: The aim of this research was to test whether social participation is associated with improvements in mood and well-being, and in particular to test whether social participation might moderate the chronic distress associated with high levels of neuroticism (N).

Method: A rural Australian sample of 394 adults (54.3% female) completed questionnaires and participated in follow-up interviews.

Changing places: the impact of rural restructuring on mental health in Australia.

Significant demographic, social and economic change has come to characterise much of rural Australia, with some authors arguing there are now two sharply differentiated zones, one of growth and one of decline. This restructuring process, which has been similar to other western nations, has had a profound impact upon rural places-socially, economically and physically. Findings from research investigating the relationship between health, place and income inequality suggest that rural 'desertification', which is characterised by decline of the agricultural sector, net population loss and the deterioration of demographic structures, may negatively influence mental health outcomes in these areas.

Rurality and mental health: the role of accessibility.

Objective: The absence of an agreed definition of "rural" limits the utility of existing research into a possible relationship between rurality of residence and mental health. The present study investigates the bipolar dimension accessibility/remoteness as a possible correlate of mental health.

Method: A continuous area of non-metropolitan Australia was selected to provide a range of scores on the Accessibility/Remoteness Index of Australia (ARIA).

Relational discrepancy theory: the implications of self discrepancy theory for dyadic relationships and for the emergence of social structure.

Relationship formation and maintenance is guided by more than similarity between partners' actual selves. Expanding the domain of self-discrepancy theory (SDT; Higgins, 1987), we propose that a type of discrepancy previously not considered-discrepancies between self-aspects of relational partners-is central to relationship cognition, including perceptions of intimacy and trust, and to the emergence of roles within relationships. Our argument relates both to unconstrained environments, where individuals freely choose partners, and constrained environments (e.