Fraction Of Peers Research Articles

Stable reputation management system in P2P networks: An evolutionary perspective

In P2P networks, peers tend to “free-ride” on the contributions of others. Many reputation-based resource sharing mechanisms have been proposed to mitigate the problem of free riding. However, the evolutionary stability of these mechanisms that require peers to keep track of the reputations of other peers has not been investigated. We show that, without any extra benefit, systems with reputation-based incentive mechanisms are not evolutionary stable. We also show that if the fraction of peers that record reputation and reciprocate accordingly is above a certain threshold, then free riding can be controlled, and a reputation management system is beneficial only when the fraction of free riders is above a certain threshold. Furthermore, we show that imposing a round-based fee and dividing it among the peers as an incentive to keep track of reputation is an evolutionary stable strategy. In this process, we analyse all the possible equilibria in different settings of the system.

Influence of peer networks on physician adoption of new drugs.

Although physicians learn about new medical technologies from their peers, the magnitude and source of peer influence is unknown. We estimate the effect of peer adoption of three first-in-class medications (dabigatran, sitigliptin, and aliskiren) on physicians’ own adoption of those medications. We included 11,958 physicians in Pennsylvania prescribing anticoagulant, antidiabetic, and antihypertensive medications. We constructed 4 types of peer networks based on shared Medicare and Medicaid patients, medical group affiliation, hospital affiliation, and medical school/residency training. Instrumental variables analysis was used to estimate the causal effect of peer adoption (fraction of peers in each network adopting the new drug) on physician adoption (prescribing at least the median number prescriptions within 15 months of the new drug’s introduction). We illustrate how physician network position can inform targeting of interventions to physicians by computing a social multiplier. Dabigatran was adopted by 25.2%, sitagliptin by 24.5% and aliskiren by 8.3% of physicians. A 10-percentage point increase in peer adoption in the patient-sharing network led to a 5.90% (SE = 1.50%, p<0.001) increase in physician adoption of dabigatran, 8.32% (SE = 1.51%, p<0.001) increase in sitagliptin, and 7.84% increase in aliskiren adoption (SE = 2.93%, p<0.001). Peer effects through shared hospital affiliation were positive but not significant, and medical group and training network effects were not reliably estimated. Physicians in the top decile of patient-sharing network peers were estimated to have nearly 2-fold stronger influence on their peers’ adoption compared to physicians in the top decile of prescribing volume. Limitations include lack of detailed clinical information and pharmaceutical promotion, variables which may influence physician adoption but which are unlikely to bias our peer effect estimates. Peer adoption, especially by those with whom physicians share patients, strongly influenced physician adoption of new drugs. Our study shows the potential for using information on physician peer networks to improve technology diffusion.

Relative peer quality and firm performance

We examine the performance impact of the relative quality of a Chief Executive Officer (CEO)’s compensation peers (peers to determine a CEO's overall compensation) and bonus peers (peers to determine a CEO's relative-performance-based bonus). We use the fraction of peers with greater managerial ability scores (Demerjian, Lev, and McVay, 2012) than the reporting firm to measure this CEO's relative peer quality (RPQ). We find that firms with higher RPQ earn higher stock returns and experience higher profitability growth than firms with lower RPQ. Learning among peers and the increased incentive to work harder induced by the peer-based tournament contribute to RPQ's performance effect.

Relative Peer Quality and Firm Performance

This study examines the performance impact of the relative quality of a CEO’s compensation peers (peers selected to determine a CEO’s overall compensation) and bonus peers (peers selected to determine a CEO’s relative-performance-based bonus). We use the fraction of peers with greater managerial ability scores (Demerjian, Lev, and McVay, 2012) than the reporting firm to measure this CEO’s relative peer quality (RPQ). We find that firms with higher RPQ tend to earn superior risk-adjusted stock returns and experience higher profitability growth compared with firms that have lower RPQ. These results cannot be fully explained by a CEO’s power, compensation level, intrinsic talent, nor by a board’s possible motivation to use peers to signal a firm’s prospect. Learning among peers and the increased incentive to work harder induced by the peer-based tournament, however, might contribute to RPQ’s positive performance effect. Preliminary evidence also shows that high RPQ is not associated with increased earnings management or increased risk-taking behaviors.

Driving in force: The influence of workplace peers on commuting decisions on U.S. military bases

We investigate the role of social influence in the commute to work. Using instruments to address the endogeneity of commute decisions and a dataset of U.S. military commuters on 100 military bases over the period 2006–2013, we show that workplace peers positively influence one another's decisions to drive alone to work and carpool to work. All else equal, an increase in the fraction of peers who drive alone of 10 percentage points increases the probability of driving alone by 6.05 percentage points. An increase in the fraction of peers who carpool of 10 percentage points increases the probability of carpooling by 5.14 percentage points. To examine whether conventional measures of social status and seniority predict who exerts the strongest influence on others, we disaggregate the dataset into subgroups and identify which subgroups have the greatest influence and which are most susceptible to influence. Results show that in commute decisions, intra-group influence can be more important than inter-group influence. This suggests that workplace travel interventions that seek to shift employees away from driving alone or toward carpooling may be most effective if communicated by one's own peer group.

Relative Peer Quality and Firm Performance

​This study examines the performance impact of the relative quality of a CEO’s compensation peers (peers selected to determine a CEO’s overall compensation) and bonus peers (peers selected to determine a CEO’s relative-performance-based bonus). We use the fraction of peers with greater managerial ability scores (Demerjian, Lev, and McVay, 2012) than the reporting firm to measure this CEO’s relative peer quality (RPQ). We find that firms with higher RPQ tend to earn superior risk-adjusted stock returns and experience higher profitability growth compared with firms that have lower RPQ. These results cannot be fully explained by a CEO’s power, compensation level, intrinsic talent, nor by the board’s possible motivation to use peers to signal a firm’s prospect. Learning among peers and the increased incentive to work harder induced by the peer-based tournament, however, might contribute to RPQ’s positive performance effect. Preliminary evidence also shows that high RPQ is not associated with increased earnings management or increased risk-taking behaviors.

Characterization of BitTorrent swarms and their distribution in the Internet

The optimization of overlay traffic resulting from applications such as BitTorrent is a challenge addressed by several recent research initiatives. However, the assessment of such optimization techniques and their performance in the real Internet remains difficult. Despite a considerable set of works measuring real-life BitTorrent swarms, several characteristics of those swarms relevant for the optimization of overlay traffic have not yet been investigated. In this work, we address this lack of realistic swarm statistics by presenting our measurement results. In particular, we provide a statistical characterization of the swarm sizes, the distribution of peers over autonomous systems (AS’s), the fraction of peers in the largest AS, and the size of the shared files. To this end, we consider different types of shared content and identify particular characteristics of regional swarms. The selection of the presented data is inspired by ongoing discussions in the IETF working group on application layer traffic optimization (ALTO). Our study is intended to provide input for the design and the assessment of ALTO solutions for BitTorrent, but the applicability of the results is not limited to that purpose.

Long Term Study of Peer Behavior in the kad DHT

Distributed hash tables (DHTs) have been actively studied in literature and many different proposals have been made on how to organize peers in a DHT. However, very few DHTs have been implemented in real systems and deployed on a large scale. One exception is KAD, a DHT based on Kademlia, which is part of eDonkey, a peer-to-peer file sharing system with several million simultaneous users. We have been crawling a representative subset of KAD every five minutes for six months and obtained information about geographical distribution of peers, session times, daily usage, and peer lifetime. We have found that session times are Weibull distributed and we show how this information can be exploited to make the publishing mechanism much more efficient. Peers are identified by the so-called KAD ID, which up to now was assumed to be persistent. However, we observed that a fraction of peers changes their KAD ID as frequently as once a session. This change of KAD IDs makes it difficult to characterize end-user behavior. For this reason we have been crawling the entire KAD network once a day for more than a year to track end-users with static IP addresses, which allows us to estimate end-user lifetime and the fraction of end-users changing their KAD ID.

An analysis of peer-to-peer networks with altruistic peers

We develop a new model of the interaction of rational peers in a Peer-to-Peer (P2P) network that has at its heart altruism, an intrinsic parameter reflecting peers’ inherent willingness to contribute. Two different approaches for modelling altruistic behavior and its attendant benefit are introduced. With either approach, we use Game Theoretic analysis to calculate Nash equilibria and predict peer behavior in terms of individual contribution. We consider the cases of P2P networks of peers that (i) have homogeneous altruism levels or (ii) have heterogeneous altruism levels, but with known probability distributions. We find that, under the effects of altruism, a substantial fraction of peers will contribute when altruism levels are within certain intervals, even though no incentive mechanism is used. Our results corroborate empirical evidence of large P2P networks surviving or even flourishing without or with barely functioning incentive mechanisms. We also enhance the model with a simple but powerful incentive scheme to limit free-riding and increase contribution to the network, and show that the particular incentive scheme on networks with altruistic peers achieves its goal.