Characterizing dynamic communication in online eating disorder communities: a multiplex network a... more Characterizing dynamic communication in online eating disorder communities: a multiplex network approach. (PDF 229 kb)
The dataset is used in the paper "Social Interactions in Online Eating Disorder Communities:... more The dataset is used in the paper "Social Interactions in Online Eating Disorder Communities: A Network Perspective".
We study a sequential trading financial market where there are gains from trade, that is, where i... more We study a sequential trading financial market where there are gains from trade, that is, where informed traders have heterogeneous private values. We show that an informational cascade (i.e., a complete blockage of information) arises and prices fail to aggregate information dispersed among traders. During an informational cascade, all traders with the same preferences choose the same action, following the market (herding) or going against it (contrarianism). We also study financial contagion by extending our model to a two-asset economy. We show that informational cascades in one market can be generated by informational spillovers from the other. Such spillovers have pathological consequences, generating long-lasting misalignments between prices and fundamentals.
The world's markets are increasingly interconnected, imposing additional challenges for both ... more The world's markets are increasingly interconnected, imposing additional challenges for both regulators and market participants. This paper considers the effect of inter-market dependencies on the spread of endogenously generated merger waves. Though merger activity can generate efficiency gains, it disrupts market competition and can lead to negative effects for consumers. The conditions under which disruptive merger activity can spread to otherwise stable markets are identified. It is also shown which inter-market dependency configurations are more likely to lead to situations in which the stability of some markets can be disrupted by merger activity in others.
We study a simple model of public opinion formation that posits that interaction between neighbou... more We study a simple model of public opinion formation that posits that interaction between neighbouring agents leads to bandwagons in the dynamics of individual opinions, as well as in that of the aggregate process. We show that in different specifications of the model, there is a tendency for the process to show consensus on one of the two competing opinions. We show how a publicly available poll of current public opinion may lead to a form of contagion, by which public opinion tends to agree with the poll. We point out that, in the absence of a poll, the process displays the feature that, after long time spans, a sequence of states occur which, when viewed locally, remain almost stationary and are characterized by large clusters of individuals of the same opinion. The running metaphor we use is that of a model of pre-electoral public opinion formation, with two candidates running. We provide some heuristic considerations on the implication that these findings could have in terms of ...
High attrition is a major problem in online health interventions. However, little is known about ... more High attrition is a major problem in online health interventions. However, little is known about risk factors of people dropping out online. Challenges exist due to the lack of baseline knowledge on how attrition naturally happens in online communities, and reliable methods that can identify causality between past traits and future dropout. Here, we examine characteristics of naturally occurring attrition in online health communities and use longitudinal statistical models to assess whether emotion and online social networks influence dropout behaviors in the future. From three comparable subpopulations sampled from Twitter, we find that individuals who self-identified as eating disordered have shorter active durations than general populations, with a half of cohort dropping out in 6 months after creating a Twitter profile. Applying instrumental variables estimation and survival analysis to longitudinal data on users’ activities spanning 1.5 year, we identify that negative emotions ...
This paper studies the analytical properties of the reinforcement learning model proposed in Erev... more This paper studies the analytical properties of the reinforcement learning model proposed in Erev and Roth (1998), also termed cumulative reinforcement learning in Laslier et al. (2001). The stochastic model of learning accounts for two main elements: the Law of E¤ect (positive reinforcement of actions that perform well) and the Power Law of Practice (learning curves tend to be steeper initially). The paper establishes a relation between the learning process and the underlying deterministic replicator equation. The main results show that if the solution trajectories of the latter converge su¢ ciently fast, then the probability that all the realizations of the learning process over a given spell of time, possibly in nite, becomes arbitrarily close to one, from some time on. In particular, the paper shows that the property of fast convergence is always satis ed in proximity of a strict Nash equilibrium. The results also provide an explicit estimate of the approximation error that coul...
We extend the model of spatial social network formation of Johnson and Gilles (Review of Economic... more We extend the model of spatial social network formation of Johnson and Gilles (Review of Economic Design, 2000, 5, 273-299) by situating each economic agent within one of a set of discrete spatial locations and allowing agents to maximise the utility that they gain from their direct and indirect social contacts by relocating, in addition to forming or breaking social links. This enables the exploration of scenarios in which agents are able to alter the distance between themselves and other agents at some cost. Agents in this model might represent countries, firms or individuals, with the distance between a pair of agents representing geographical, social or individual differences. The network of social relationships characterises some form of self-organised persistent interaction such as trade agreements or friendship patterns. By varying the distance-dependent costs of relocation and maintaining social relationships we are able to identify conditions that promote the formation of s...
The benefits of money as a medium of exchange are obvious, but existing models of monetary search... more The benefits of money as a medium of exchange are obvious, but existing models of monetary search fail to account for the separate relationships that agents develop between providers and acceptors of money. In this paper, the Kiyotaki-Wright model of monetary search is reproduced as small population agent-based model, and the random matching rule is replaced by a weighted matching model where the probability of successful trades is adaptively reinforced over time. Results show the endogenous emergence of stable patterns of networked trade transactions.
We study a simple model of pre-electoral opinion formation that posits that interaction between n... more We study a simple model of pre-electoral opinion formation that posits that interaction between neighbouring voters leads to bandwagons in the dynamics of the individual process, as well as in that of the aggregate process. We show that in di¤erent speci...cations of the model, there is a tendency for the process to show consensus, i.e. to approach a con...guration of homogeneous support for one candidate, out of the two who run the electoral campaign. We point out that the process displays the feature that, after long time spans, a sequence of states occur which, when viewed locally, remain almost stationary and are characterized by large clusters of individuals of the same opinion. ¤JEL: D72, D82, C44.
We investigate the behavior of some locally interactive learning systems for a finite population ... more We investigate the behavior of some locally interactive learning systems for a finite population of players. We assume that each player is matched with his neighboring players to play a coordination game. Players adopt boundedly rational rules of behavior and update their strategy choices with inertia. Learning and experimentation are entirely motivated by payoff considerations. We analyze the asymptotic properties of the aggregate system, and we prove convergence to absorbing states, which we characterize. We report on the results of some simulations carried out on a cellular automaton hardware board that simulates a torus of size 256×256 at a speed of 60 frames per second.
Erev and Roth (1998) among others provide a comprehensive analysis of experimental evidence on le... more Erev and Roth (1998) among others provide a comprehensive analysis of experimental evidence on learning in games, based on a stochastic model of learning that accounts for two main elements: the Law of Effect (positive reinforcement of actions that perform well) and the Power Law of Practice (learning curves tend to be steeper initially). This note complements this literature by providing an analytical study of the properties of such learning models. Specifically, the paper shows that: a) up to an error term, the stochastic process is driven by a system of discrete time difference equations of the replicator type. This carries an analogy with Börgers and Sarin (1997), where reinforcement learning accounts only for the Law of Effect. b) if the trajectories of the system of replicator equations converge sufficiently fast, then the probability that all realizations of the learning process over a possibly infinite spell of time lie within a given small distance of the solution path of t...
Background The use of social media as a key health information source has increased steadily amon... more Background The use of social media as a key health information source has increased steadily among people affected by eating disorders (EDs). Research has examined characteristics of individuals engaging in online communities, whereas little is known about discontinuation of engagement and the phenomenon of participants dropping out of these communities. Objective This study aimed to investigate the characteristics of dropout behaviors among eating disordered individuals on Twitter and to estimate the causal effects of personal emotions and social networks on dropout behaviors. Methods Using a snowball sampling method, we collected a set of individuals who self-identified with EDs in their Twitter profile descriptions, as well as their tweets and social networks, leading to 241,243,043 tweets from 208,063 users. Individuals’ emotions are measured from their language use in tweets using an automatic sentiment analysis tool, and network centralities are measured from users’ following ...
Characterizing dynamic communication in online eating disorder communities: a multiplex network a... more Characterizing dynamic communication in online eating disorder communities: a multiplex network approach. (PDF 229 kb)
The dataset is used in the paper "Social Interactions in Online Eating Disorder Communities:... more The dataset is used in the paper "Social Interactions in Online Eating Disorder Communities: A Network Perspective".
We study a sequential trading financial market where there are gains from trade, that is, where i... more We study a sequential trading financial market where there are gains from trade, that is, where informed traders have heterogeneous private values. We show that an informational cascade (i.e., a complete blockage of information) arises and prices fail to aggregate information dispersed among traders. During an informational cascade, all traders with the same preferences choose the same action, following the market (herding) or going against it (contrarianism). We also study financial contagion by extending our model to a two-asset economy. We show that informational cascades in one market can be generated by informational spillovers from the other. Such spillovers have pathological consequences, generating long-lasting misalignments between prices and fundamentals.
The world's markets are increasingly interconnected, imposing additional challenges for both ... more The world's markets are increasingly interconnected, imposing additional challenges for both regulators and market participants. This paper considers the effect of inter-market dependencies on the spread of endogenously generated merger waves. Though merger activity can generate efficiency gains, it disrupts market competition and can lead to negative effects for consumers. The conditions under which disruptive merger activity can spread to otherwise stable markets are identified. It is also shown which inter-market dependency configurations are more likely to lead to situations in which the stability of some markets can be disrupted by merger activity in others.
We study a simple model of public opinion formation that posits that interaction between neighbou... more We study a simple model of public opinion formation that posits that interaction between neighbouring agents leads to bandwagons in the dynamics of individual opinions, as well as in that of the aggregate process. We show that in different specifications of the model, there is a tendency for the process to show consensus on one of the two competing opinions. We show how a publicly available poll of current public opinion may lead to a form of contagion, by which public opinion tends to agree with the poll. We point out that, in the absence of a poll, the process displays the feature that, after long time spans, a sequence of states occur which, when viewed locally, remain almost stationary and are characterized by large clusters of individuals of the same opinion. The running metaphor we use is that of a model of pre-electoral public opinion formation, with two candidates running. We provide some heuristic considerations on the implication that these findings could have in terms of ...
High attrition is a major problem in online health interventions. However, little is known about ... more High attrition is a major problem in online health interventions. However, little is known about risk factors of people dropping out online. Challenges exist due to the lack of baseline knowledge on how attrition naturally happens in online communities, and reliable methods that can identify causality between past traits and future dropout. Here, we examine characteristics of naturally occurring attrition in online health communities and use longitudinal statistical models to assess whether emotion and online social networks influence dropout behaviors in the future. From three comparable subpopulations sampled from Twitter, we find that individuals who self-identified as eating disordered have shorter active durations than general populations, with a half of cohort dropping out in 6 months after creating a Twitter profile. Applying instrumental variables estimation and survival analysis to longitudinal data on users’ activities spanning 1.5 year, we identify that negative emotions ...
This paper studies the analytical properties of the reinforcement learning model proposed in Erev... more This paper studies the analytical properties of the reinforcement learning model proposed in Erev and Roth (1998), also termed cumulative reinforcement learning in Laslier et al. (2001). The stochastic model of learning accounts for two main elements: the Law of E¤ect (positive reinforcement of actions that perform well) and the Power Law of Practice (learning curves tend to be steeper initially). The paper establishes a relation between the learning process and the underlying deterministic replicator equation. The main results show that if the solution trajectories of the latter converge su¢ ciently fast, then the probability that all the realizations of the learning process over a given spell of time, possibly in nite, becomes arbitrarily close to one, from some time on. In particular, the paper shows that the property of fast convergence is always satis ed in proximity of a strict Nash equilibrium. The results also provide an explicit estimate of the approximation error that coul...
We extend the model of spatial social network formation of Johnson and Gilles (Review of Economic... more We extend the model of spatial social network formation of Johnson and Gilles (Review of Economic Design, 2000, 5, 273-299) by situating each economic agent within one of a set of discrete spatial locations and allowing agents to maximise the utility that they gain from their direct and indirect social contacts by relocating, in addition to forming or breaking social links. This enables the exploration of scenarios in which agents are able to alter the distance between themselves and other agents at some cost. Agents in this model might represent countries, firms or individuals, with the distance between a pair of agents representing geographical, social or individual differences. The network of social relationships characterises some form of self-organised persistent interaction such as trade agreements or friendship patterns. By varying the distance-dependent costs of relocation and maintaining social relationships we are able to identify conditions that promote the formation of s...
The benefits of money as a medium of exchange are obvious, but existing models of monetary search... more The benefits of money as a medium of exchange are obvious, but existing models of monetary search fail to account for the separate relationships that agents develop between providers and acceptors of money. In this paper, the Kiyotaki-Wright model of monetary search is reproduced as small population agent-based model, and the random matching rule is replaced by a weighted matching model where the probability of successful trades is adaptively reinforced over time. Results show the endogenous emergence of stable patterns of networked trade transactions.
We study a simple model of pre-electoral opinion formation that posits that interaction between n... more We study a simple model of pre-electoral opinion formation that posits that interaction between neighbouring voters leads to bandwagons in the dynamics of the individual process, as well as in that of the aggregate process. We show that in di¤erent speci...cations of the model, there is a tendency for the process to show consensus, i.e. to approach a con...guration of homogeneous support for one candidate, out of the two who run the electoral campaign. We point out that the process displays the feature that, after long time spans, a sequence of states occur which, when viewed locally, remain almost stationary and are characterized by large clusters of individuals of the same opinion. ¤JEL: D72, D82, C44.
We investigate the behavior of some locally interactive learning systems for a finite population ... more We investigate the behavior of some locally interactive learning systems for a finite population of players. We assume that each player is matched with his neighboring players to play a coordination game. Players adopt boundedly rational rules of behavior and update their strategy choices with inertia. Learning and experimentation are entirely motivated by payoff considerations. We analyze the asymptotic properties of the aggregate system, and we prove convergence to absorbing states, which we characterize. We report on the results of some simulations carried out on a cellular automaton hardware board that simulates a torus of size 256×256 at a speed of 60 frames per second.
Erev and Roth (1998) among others provide a comprehensive analysis of experimental evidence on le... more Erev and Roth (1998) among others provide a comprehensive analysis of experimental evidence on learning in games, based on a stochastic model of learning that accounts for two main elements: the Law of Effect (positive reinforcement of actions that perform well) and the Power Law of Practice (learning curves tend to be steeper initially). This note complements this literature by providing an analytical study of the properties of such learning models. Specifically, the paper shows that: a) up to an error term, the stochastic process is driven by a system of discrete time difference equations of the replicator type. This carries an analogy with Börgers and Sarin (1997), where reinforcement learning accounts only for the Law of Effect. b) if the trajectories of the system of replicator equations converge sufficiently fast, then the probability that all realizations of the learning process over a possibly infinite spell of time lie within a given small distance of the solution path of t...
Background The use of social media as a key health information source has increased steadily amon... more Background The use of social media as a key health information source has increased steadily among people affected by eating disorders (EDs). Research has examined characteristics of individuals engaging in online communities, whereas little is known about discontinuation of engagement and the phenomenon of participants dropping out of these communities. Objective This study aimed to investigate the characteristics of dropout behaviors among eating disordered individuals on Twitter and to estimate the causal effects of personal emotions and social networks on dropout behaviors. Methods Using a snowball sampling method, we collected a set of individuals who self-identified with EDs in their Twitter profile descriptions, as well as their tweets and social networks, leading to 241,243,043 tweets from 208,063 users. Individuals’ emotions are measured from their language use in tweets using an automatic sentiment analysis tool, and network centralities are measured from users’ following ...
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