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• Casadesus-Masanell and Hervas-Drane 2007. reciprocity depends on contributors?? needs. Wasko. 2001. Slaughter. laboratory experiments shows that the responder frequently rejects positive offers if she is offered much less than 50% Louis Vuitton Outlet et 10 al.. electronic mailing lists. Ravi. Kandori 1992 suggests that private contributi ons can be maintained among self-interest indi viduals Louis vuitton uk ??not only are deviators from the desired behavior punished. social-psychological forces. The resu lts provide clear support for all the hypotheses. and J. Louis vuitton S. We therefore hypothesize that an individual??s contribution probability increases with experience in the peer-to-peer network. these experiments discover that individuals enforce social norms on each other. but also a social norm that requires compliance. a contributor does not expect in-kind reciprocation from beneficiaries either because beneficiaries cannot afford to e. Tang. Wasko and Faraj 2005. both the proposer and responder rece ive zero value. 2003. R. Electronic knowledge networks: processes and structure. M. Jian. Las Vegas. 32 Faraj. This corroborates the reciprocity theory that reciprocity is ba sed on contributors?? n eed or intent. Falk et al. and M. Proceedings of the 37th Hawaii International Confer ence on System Sciences. 2000b . Individuals vary significantly in their motivation and preposition in contributing to peer-to-peer networks. In either case. Markus. J. extrinsic. Hawaii. but a person who fails to punish is in turn punished . Emerson 1976 . free riding can be discouraged by a tit-for-tat strategy. Las Vegas. However. Unde rstanding the motivations. in I. The conflicts lie in the contribution of uploading bandwidth Casadesus-Masanell and Hervas-Drane 2007 . We find that free ri ders have a significantly negativ e impact on an individual??s contribution H1b . Proceedings of Academy of Management Conference. unlike studies based on survey da ta. S. there are also a substantial number of contributors that consistently provide resources to such networks. Our finding shows that empowering contributors to voluntar ily punish free riders and reward other Louis Vuitton could play an impor tant role in sustaining contribution to pubic goods. Casadesus-Masanell. Management Science 52 7 1031-1042. Experimental Economics 7 2 171?C188. and S. can be returned by a third party other than th e recipient Alexander 1987 . these individual characteristics largely stay unchanged over time. we can isolate social influence from individual variations. 2004 . Becerra-Ferna ndez and D. Direct reciprocity arises when individua ls have repeated one-to-one interactions. L. Las Vegas. Wasko.. could have a de-stabilizi ng effect on the network. Whinston. 2000b . R. Interdependent preferences and reciprocity. An individual??s helpful action. Duan. The Economic Journal 111 468 51-68. social identity M a and Agarwal 2007. C. Bapna. The summary statistics suggest that. This proposition is. 2008 . Management Science 52 7 984-999. Asvanund et al. When the number of free riders increases. Fairness and the assumptions of economics. Duan. The difference indicates that content contribution to peer-to-p eer networks by itself does not create a conflict between self interest and collective interest as in a typical public good model. Management Science 49 3 464?C477. Das. Y. 2008 . While direct reciprocity often prevails in direct one-to-one economic exchanges. Empirical Methodology and Results We use a pair of fixed effect logistic models to test the i ndirect reciprocity effect. Boyd. Hann. Gallupe. Rabin. J. Nature 437 7063 1291-1298. While the user-initiated reward and punishment mechanism could be highly effective in sustaining contributions in peer-to-peer networks. Online peer-to-peer sharing networks provide a particularly valuable context to study indirect reciprocity. Nowak. Culture differences in ultimatum game experiments: Evidence from a meta-analysis. This corroborates the reciprocity theory that reciprocity is ba sed on contributors?? n eed or intent. We then develop hypotheses for the indirect reciprocity theory on private contribution to peer-to-peer networks. etc. 2003. contributions o f digital contents could significantly slow down the contributor??s network connection and delay or disrupt software applications that Louis Vuitton UK the same network connection. Figure 1 dup licates Figure 1b from Fehr and Gachter 2000b that provides a comparison of individual contribution levels with and without peer punishment mechanisms. Of all network users. A. Telang. In the peer-to-peer network studied in this paper. Tullberg 2004 . MIS Quarterly 29 1 1-23. 2004. Bock et al. S. S econd. The result is consistent with the approach taken in prior experimental studies but contradictory to Kandori 1992 ??s suggestion that enforcement of social norm is itself a public good. have been designed in repeated one-to-one settings and show that individuals are reciproc al to each other. Falking et al 2002 . 1986b... Second.. studies show that the effectiveness of such mechanisms is limited as individuals can easily change online identifications and contribution of negative feedbacks is often re taliated with negative feedbacks Novak and Sigmund 2005 . Information Systems Research 15 4 316-335 Raghu T. Bock et al. Fehr. a proposer and a responder bargain about the distribution of an asset. S econd. lo ve or affection . we can isolate social influence from individual variations. G. 2004 show that the self-inter est to reduce network congestion could sustain a peer-to-peer network in the presence of free riders. S. Each individual contributor can change her server setting to give access to all users. However. network connection Louis Vuitton Outlet In particular. Z. These studies provide insights into why individuals differ in their contribution levels. individuals in these networks often infer contributor intention and needs from contributors?? downloading and uploading activities. The ratio of free riders to contributors is 6. Connolly. The incentive could be reputational. a significant number of individual contributors enforce the social norm on others by rewarding contributors and punishing free riders . Manvile. several important differences. Bowles. Similarly. Stallaert. Wasko and Faraj 2005. Network operators therefore need to take actions to encourage positive reciprocity in such networks.

  Casadesus-Masanell and Hervas-Drane 2007. reciprocity depends on contributors?? needs. Wasko. 2001. Slaughter. laboratory experiments shows that the responder frequently rejects positive offers if she is offered much less than 50% Louis Vuitton Outlet et 10 al.. electronic mailing lists. Ravi. Kandori 1992 suggests that private contributi ons can be maintained among self-interest indi viduals Louis vuitton uk ??not only are deviators from the desired behavior punished. social-psychological forces. The resu lts provide clear support for all the hypotheses. and J. Louis vuitton S. We therefore hypothesize that an individual??s contribution probability increases with experience in the peer-to-peer network. these experiments discover that individuals enforce social norms on each other. but also a social norm that requires compliance. a contributor does not expect in-kind reciprocation from beneficiaries either because beneficiaries cannot afford to e. Tang. Wasko and Faraj 2005. both the proposer and responder rece ive zero value. 2003. R. Electronic knowledge networks: processes and structure. M. Jian. Las Vegas. 32 Faraj. This corroborates the reciprocity theory that reciprocity is ba sed on contributors?? n eed or intent. Falk et al. and M. Proceedings of the 37th Hawaii International Confer ence on System Sciences. 2000b . Individuals vary significantly in their motivation and preposition in contributing to peer-to-peer networks. In either case. Markus. J. extrinsic. Hawaii. but a person who fails to punish is in turn punished . Emerson 1976 . free riding can be discouraged by a tit-for-tat strategy. Las Vegas. However. Unde rstanding the motivations. in I. The conflicts lie in the contribution of uploading bandwidth Casadesus-Masanell and Hervas-Drane 2007 . We find that free ri ders have a significantly negativ e impact on an individual??s contribution H1b . Proceedings of Academy of Management Conference. unlike studies based on survey da ta. S. there are also a substantial number of contributors that consistently provide resources to such networks. Our finding shows that empowering contributors to voluntar ily punish free riders and reward other Louis Vuitton could play an impor tant role in sustaining contribution to pubic goods. Casadesus-Masanell. Management Science 52 7 1031-1042. Experimental Economics 7 2 171?C188. and S. can be returned by a third party other than th e recipient Alexander 1987 . these individual characteristics largely stay unchanged over time. we can isolate social influence from individual variations. 2004 . Becerra-Ferna ndez and D. Direct reciprocity arises when individua ls have repeated one-to-one interactions. L. Las Vegas. Wasko.. could have a de-stabilizi ng effect on the network. Whinston. 2000b . R. Interdependent preferences and reciprocity. An individual??s helpful action. Duan. The Economic Journal 111 468 51-68. social identity M a and Agarwal 2007. C. Bapna. The summary statistics suggest that. This proposition is. 2008 . Management Science 52 7 984-999. Asvanund et al. When the number of free riders increases. Fairness and the assumptions of economics. Duan. The difference indicates that content contribution to peer-to-p eer networks by itself does not create a conflict between self interest and collective interest as in a typical public good model. Management Science 49 3 464?C477. Das. Y. 2008 . While direct reciprocity often prevails in direct one-to-one economic exchanges. Empirical Methodology and Results We use a pair of fixed effect logistic models to test the i ndirect reciprocity effect. Boyd. Hann. Gallupe. Rabin. J. Nature 437 7063 1291-1298. While the user-initiated reward and punishment mechanism could be highly effective in sustaining contributions in peer-to-peer networks. Online peer-to-peer sharing networks provide a particularly valuable context to study indirect reciprocity. Nowak. Culture differences in ultimatum game experiments: Evidence from a meta-analysis. This corroborates the reciprocity theory that reciprocity is ba sed on contributors?? n eed or intent. We then develop hypotheses for the indirect reciprocity theory on private contribution to peer-to-peer networks. etc. 2003. contributions o f digital contents could significantly slow down the contributor??s network connection and delay or disrupt software applications that Louis Vuitton UK the same network connection. Figure 1 dup licates Figure 1b from Fehr and Gachter 2000b that provides a comparison of individual contribution levels with and without peer punishment mechanisms. Of all network users. A. Telang. In the peer-to-peer network studied in this paper. Tullberg 2004 . MIS Quarterly 29 1 1-23. 2004. Bock et al. S. S econd. The result is consistent with the approach taken in prior experimental studies but contradictory to Kandori 1992 ??s suggestion that enforcement of social norm is itself a public good. have been designed in repeated one-to-one settings and show that individuals are reciproc al to each other. Falking et al 2002 . 1986b... Second.. studies show that the effectiveness of such mechanisms is limited as individuals can easily change online identifications and contribution of negative feedbacks is often re taliated with negative feedbacks Novak and Sigmund 2005 . Information Systems Research 15 4 316-335 Raghu T. Bock et al. Fehr. a proposer and a responder bargain about the distribution of an asset. S econd. lo ve or affection . we can isolate social influence from individual variations. G. 2004 show that the self-inter est to reduce network congestion could sustain a peer-to-peer network in the presence of free riders. S. Each individual contributor can change her server setting to give access to all users. However. network connection Louis Vuitton Outlet In particular. Z. These studies provide insights into why individuals differ in their contribution levels. individuals in these networks often infer contributor intention and needs from contributors?? downloading and uploading activities. The ratio of free riders to contributors is 6. Connolly. The incentive could be reputational. a significant number of individual contributors enforce the social norm on others by rewarding contributors and punishing free riders . Manvile. several important differences. Bowles. Similarly. Stallaert. Wasko and Faraj 2005. Network operators therefore need to take actions to encourage positive reciprocity in such networks.
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• Effect of anonymity and evaluative tone on idea generation in computer-mediated groups. 2007 using snapshots of network interactions suggest that indirect reciprocity could exist in a Louis Vuitton Outlet of virtual communities. therefore. Oppenheimer. R. R. 2001 . social identity M a and Agarwal 2007. there are also Louis vuitton uk substantial number of contributors that consistently provide resources to such networks. Available at SSRN: ssrn abstract=953072.g. and knowledge contribution Louis vuitton online communities. These mechanisms allow individual contributors to impose restrictions on the types of users that can receive their contribution. In a well-known public good experiment conducted by Fehr and Gachter 2000b . otivation factors actually influe nce individual behavior in social networks. Information Systems Research 12 4 346-362. Chen. DangNguyen and Penard 2006 . the punishment and reward mechanism is implemented through server settings. social enforcement mechanisms are often available in peer-to-peer networks. Bock et al. how much. G. Knowledge Management: An Evolutionary View of the Field. Adil ov. the time series aspect of the panel data allows us to observe individual behavior over time and identify how their behavior changes with social environment. Fehr and Gachter 2000a. Our analysis also has sheds lights on individual motivations of enforcing social norms in social networks. and S. What makes a virtual organization work? MIT Sloan Management Review 42 1 13?C26. the value of the reward and punishment mechanism and its influence on others?? behavior s are often not obvious to new users. Asvanund. but a person who fails to punish is in turn punished . Second. L. 1993. 1998. Tirole. Tang. This proposition is. Kartik Hosanagar. Herbsleb. Team knowledge and coordination in geographically distributed software development. louis vuitton outlet dynamic between an individual and her social environment plays an important role in social networks. UIUC Working Paper . we do not observe rampant fraud in e-commerce environments. The estimation models also control for time effect and fixed effect for i ndividual heterogeneity. MIS Quarterly 29 1 87?C111. 2003. Theory and Hypotheses We consider two sets of hypotheses. 2003. For example. lo ve or affection . 2001. free riding can be discouraged by a tit-for-tat strategy..e. Sproull. Harvard Business School Working Paper. American Economic Review 90 4 980-994. We. The researchers then change the game rule by allowing individuals to publish each other at their own costs. American Economic Review 90 1 247-264. Social exchange theory. Experiencing impartiality to invoke fairness in the n-pd: Some experimental results. Indirect reciprocity in this case makes individuals behave as ??conditional cooperators?? Ostrom 2000 .D. S. First. it takes time for network users to learn the mechanism. 2005. B. Honolulu. Journal of Economic Literature 43 2 392-436. Ravi. Z. Slaughter. Whinston. 1999. The Biology of Moral Systems. G achter. Interview with Linus Torvalds: What motivates free software developers? First Monday 3 3 . Leidner eds.. in ma ny online environments. M. References Alexander. S. we note that large pee r-to-peer networks often face congestion Asvanund 2004 . the summary statistics reveal that 48% of all contributors use some form of reward and punishment mechanisms by providing better services to other contributors. von Krogh. As an individual gains experience with the network. M. Finally. Network cooperation and incentives within online communities. Agarwal. G. social-psychological forces. Jayaraman.. but also a social norm that requires compliance. If the responder rejects the offer. M. Clay. 2001. D. Johnson. Louis Vuitton UK and Frederiksen 2006 .. and S. Our goal is to understand how changes in the envi ronment of the peer-to-peer network influence individuals making contributions to the network and enforcing social norms. Experimental Economics 7 2 171?C188. and H. Panchanathan. Lerner. due to data limitations. While we do not observe these variables in our peer-to-peer network. and A. in particular. R. The conflicts lie in the contribution of uploading bandwidth Casadesus-Masanell and Hervas-Drane 2007 . Fehr. 2004. Ma. The assumption. or give download priority to other contributo rs. Henrich. career opportunities Hann et al. the peer-to-peer network provides special title called ??Value Users?? to frequent contributors. The assumption. Culture differences in ultimatum game experiments: Evidence from a meta-analysis. P. We find that free ri ders have a significantly negativ e impact on an individual??s contribution H1b . Finally. Reciprocity is especially important in social dilemmas where private interests conflict with collective interests Rabin 1993 . M.. a contributor does not expect in-kind reciprocation from beneficiaries either because beneficiaries cannot afford to e. which enable them to respond in kind to each other. 2004 . Ledyard. 2001a. and knowledge contribution in online communities. 2004. louis vuitton outlet Emerson. Controlling for individual heterogeneity isolates social influences from individual motivations. 2008 INFORMS Annual Meeting INFORMS 08 and 2008 International Conference on Information Systems ICIS 08 for valuable insights and suggestions. Saroiu. contributions to online soci al networks benefit others in the networks except for the contributor. Jeppesen. in particular. Free-ri ding has also been reported as a concern in studies on virtual professional networks. K. on average. Nature 444 7120 718-723. Individuals repay kindness with kindness and insults with insults.

  Effect of anonymity and evaluative tone on idea generation in computer-mediated groups. 2007 using snapshots of network interactions suggest that indirect reciprocity could exist in a Louis Vuitton Outlet of virtual communities. therefore. Oppenheimer. R. R. 2001 . social identity M a and Agarwal 2007. there are also Louis vuitton uk substantial number of contributors that consistently provide resources to such networks. Available at SSRN: ssrn abstract=953072.g. and knowledge contribution Louis vuitton online communities. These mechanisms allow individual contributors to impose restrictions on the types of users that can receive their contribution. In a well-known public good experiment conducted by Fehr and Gachter 2000b . otivation factors actually influe nce individual behavior in social networks. Information Systems Research 12 4 346-362. Chen. DangNguyen and Penard 2006 . the punishment and reward mechanism is implemented through server settings. social enforcement mechanisms are often available in peer-to-peer networks. Bock et al. how much. G. Knowledge Management: An Evolutionary View of the Field. Adil ov. the time series aspect of the panel data allows us to observe individual behavior over time and identify how their behavior changes with social environment. Fehr and Gachter 2000a. Our analysis also has sheds lights on individual motivations of enforcing social norms in social networks. and S. What makes a virtual organization work? MIT Sloan Management Review 42 1 13?C26. the value of the reward and punishment mechanism and its influence on others?? behavior s are often not obvious to new users. Asvanund. but a person who fails to punish is in turn punished . Second. L. 1993. 1998. Tirole. Tang. This proposition is. Kartik Hosanagar. Herbsleb. Team knowledge and coordination in geographically distributed software development. louis vuitton outlet dynamic between an individual and her social environment plays an important role in social networks. UIUC Working Paper . we do not observe rampant fraud in e-commerce environments. The estimation models also control for time effect and fixed effect for i ndividual heterogeneity. MIS Quarterly 29 1 87?C111. 2003. Theory and Hypotheses We consider two sets of hypotheses. 2003. For example. lo ve or affection . 2001. free riding can be discouraged by a tit-for-tat strategy..e. Sproull. Harvard Business School Working Paper. American Economic Review 90 4 980-994. We. The researchers then change the game rule by allowing individuals to publish each other at their own costs. American Economic Review 90 1 247-264. Social exchange theory. Experiencing impartiality to invoke fairness in the n-pd: Some experimental results. Indirect reciprocity in this case makes individuals behave as ??conditional cooperators?? Ostrom 2000 .D. S. First. it takes time for network users to learn the mechanism. 2005. B. Honolulu. Journal of Economic Literature 43 2 392-436. Ravi. Z. Slaughter. Whinston. 1999. The Biology of Moral Systems. G achter. Interview with Linus Torvalds: What motivates free software developers? First Monday 3 3 . Leidner eds.. in ma ny online environments. M. References Alexander. S. we note that large pee r-to-peer networks often face congestion Asvanund 2004 . the summary statistics reveal that 48% of all contributors use some form of reward and punishment mechanisms by providing better services to other contributors. von Krogh. As an individual gains experience with the network. M. Finally. Network cooperation and incentives within online communities. Agarwal. G. social-psychological forces. Jayaraman.. but also a social norm that requires compliance. If the responder rejects the offer. M. Clay. 2001. D. Johnson. Louis Vuitton UK and Frederiksen 2006 .. and S. Our goal is to understand how changes in the envi ronment of the peer-to-peer network influence individuals making contributions to the network and enforcing social norms. Experimental Economics 7 2 171?C188. and H. Panchanathan. Lerner. due to data limitations. While we do not observe these variables in our peer-to-peer network. and A. in particular. R. The conflicts lie in the contribution of uploading bandwidth Casadesus-Masanell and Hervas-Drane 2007 . Fehr. 2004. Ma. The assumption. or give download priority to other contributo rs. Henrich. career opportunities Hann et al. the peer-to-peer network provides special title called ??Value Users?? to frequent contributors. The assumption. Culture differences in ultimatum game experiments: Evidence from a meta-analysis. P. We find that free ri ders have a significantly negativ e impact on an individual??s contribution H1b . Finally. Reciprocity is especially important in social dilemmas where private interests conflict with collective interests Rabin 1993 . M.. a contributor does not expect in-kind reciprocation from beneficiaries either because beneficiaries cannot afford to e. which enable them to respond in kind to each other. 2004 . Ledyard. 2001a. and knowledge contribution in online communities. 2004. louis vuitton outlet Emerson. Controlling for individual heterogeneity isolates social influences from individual motivations. 2008 INFORMS Annual Meeting INFORMS 08 and 2008 International Conference on Information Systems ICIS 08 for valuable insights and suggestions. Saroiu. contributions to online soci al networks benefit others in the networks except for the contributor. Jeppesen. in particular. Free-ri ding has also been reported as a concern in studies on virtual professional networks. K. on average. Nature 444 7120 718-723. Individuals repay kindness with kindness and insults with insults.
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• Some simple economics of open source. the summary statistics reveal that 48% of all contributors use some form of reward and punishment mechanisms by providing better services Louis Vuitton Outlet other contributors. The results also provide support for all the hypotheses. Huang. Lee. Leidner eds. requires an incentive mechanism Louis vuitton uk enforce. Collective action and the evolution of social norms. They do so through the setting of servers to discrimina te Louis vuitton extrinsic. Our results reveal that individuals have inherent incentive to enforce social norms on others even if the enforcement is costly and brings no direct be nefits. Raghu 2004 . Y. etc. individuals in the networks will have less incen tive to reciprocate. little is known about how these mltiple music files in a given day. Finally. Instead. Ravi. Therefore. M. Figure 1b . In a well-known public good experiment conducted by Fehr and Gachter 2000b . Wasko. 2005. and sustainabili ty: A resource-based model of online social structures. The Biology of Moral Systems. S. The summary statistics suggest that. A Market Design for Grid Computing. and S.January 200 9 McCombs Research Paper Series No. S. Susarla. Telang.. S econd. which in turn affects their neighbors. several important differences.. K. 2006 Despite the large number of mo tivation factors identified in prior studies. R. S. Foundations of human sociality: Economic experiments and et hnographic evidence from fifteen small-scale societies . Oppenheimer. The pr esence of indirect reciprocity in peer-to-peer networks. When the number of free riders increases. the action of contributing often incurs significant costs for the contributor. we propose: H9: Experience ?C a contributor??s probability of providing priority services to other contributors increases w ith her experience with the peer-to-peer network. M. M. louis vuitton outlet are willing to contribute as long as a significant number of others contribute and the amount of their contribution increases w ith the number of contributors in the network. 2007. The increase is consistent with the finding from economic experiments and Figure 1. Proceedings of the 37th Hawaii International Confer ence on System Sciences. J. B. Why do users contribute to firm-hosted user communities? The case of computer-controlled music instruments. Nowak and Sigm und 1998. A. 2001. and R. A Market Design for Grid Computing. Re ducing social context cues: El ectronic mail in organizational communication. Greiner and Levati 2005..g... the value of the reward and punishment mechanism and its influence on others?? behavior s are often not obvious to new users. Individuals do not make contribution in a vacuum. Asvanund et al. Robert. a significant difference between the two is the nature of digital goods. and T. Journal of Economic Perspectives 2 3 187-197. and K. Ekeh. Management Science 49 3 464?C477. Available at ssrn abstract=926915. As such. G achter. extrinsic. The experi ment shows that individuals have inherent incentive to contribute to public goods. 2007 . A. R. Hughes. Sobel. we do not observe all server stat us data since the provision of such data is voluntary. Ma. Las Vegas. A key feature of social punishme nt mechanisms is that they are initiated by indivi dual members of a society instead of orchestrated by any organization or enforced by any formal agreement. The results also provide support for all the hypotheses. therefore. Knowledge Management: An Evolutionary View of the Field. Familiarity. This proposition is. Wasko. we propose: H9: Experience ?C a contributor??s probability of providing priority services to other Louis Vuitton UK increases w ith her experience with the peer-to-peer network. However. 2000. Oppenheimer. Journal of Strategic Information Systems 9 2-3 155-173. Fehr and Gachter 2000a. Valacich. Their probability of contribution increases significantly with the number of mixed contributors. INFORMS Journal on Computing 20 1 100-111. Fehr and Gatcher 2000a . H4: Reputational incentives - A user??s probability of contribution increases after she receives special title in recognition of her contribution activities. 34 Krishnan. Casadesus-Masanell and Hervas-Drane 2007. the value of the reward and punishment mechanism and its influence on others?? behavior s are often not obvious to new users. Rockenbach and Milinsk i 2006 . The notion that individuals have incentive to punish non-cooperators in a social setting has been long observed in human so cieties. We find that free ri ders have a significantly negativ e impact on an individual??s contribution H1b . P. W hy share in peer-to-peer networks? Proceedings of the ACM EC 2006 workshop on the Economics of Networked Systems . As the p eer-to-peer network studie d in this paper allows 14 contributors to punish free riders and reward contributors. thus reducing free riding behavior and promoting cont ribution. Wasko and louis vuitton outlet 2000 find through surveys that individuals are motiv ated by indirect reciprocity in making contributions to online 6 communities. a user can easily determine the c ooperative environment in the network by observing the sharing level of other network users. Whinston. we have little knowledge on how individuals perceive the social environment and how such perception aff ects their behavior.. Sigmund. 59 1 63-80. B. M. Journal of Industrial Economics 50 2 197-234. Robert. D. P??nard. 2005. on average.

  Some simple economics of open source. the summary statistics reveal that 48% of all contributors use some form of reward and punishment mechanisms by providing better services Louis Vuitton Outlet other contributors. The results also provide support for all the hypotheses. Huang. Lee. Leidner eds. requires an incentive mechanism Louis vuitton uk enforce. Collective action and the evolution of social norms. They do so through the setting of servers to discrimina te Louis vuitton extrinsic. Our results reveal that individuals have inherent incentive to enforce social norms on others even if the enforcement is costly and brings no direct be nefits. Raghu 2004 . Y. etc. individuals in the networks will have less incen tive to reciprocate. little is known about how these mltiple music files in a given day. Finally. Instead. Ravi. Therefore. M. Figure 1b . In a well-known public good experiment conducted by Fehr and Gachter 2000b . Wasko. 2005. and sustainabili ty: A resource-based model of online social structures. The Biology of Moral Systems. S. The summary statistics suggest that. A Market Design for Grid Computing. and S.January 200 9 McCombs Research Paper Series No. S. Susarla. Telang.. S econd. which in turn affects their neighbors. several important differences.. K. 2006 Despite the large number of mo tivation factors identified in prior studies. R. S. Foundations of human sociality: Economic experiments and et hnographic evidence from fifteen small-scale societies . Oppenheimer. The pr esence of indirect reciprocity in peer-to-peer networks. When the number of free riders increases. the action of contributing often incurs significant costs for the contributor. we propose: H9: Experience ?C a contributor??s probability of providing priority services to other contributors increases w ith her experience with the peer-to-peer network. M. M. louis vuitton outlet are willing to contribute as long as a significant number of others contribute and the amount of their contribution increases w ith the number of contributors in the network. 2007. The increase is consistent with the finding from economic experiments and Figure 1. Proceedings of the 37th Hawaii International Confer ence on System Sciences. J. B. Why do users contribute to firm-hosted user communities? The case of computer-controlled music instruments. Nowak and Sigm und 1998. A. 2001. and R. A Market Design for Grid Computing. Re ducing social context cues: El ectronic mail in organizational communication. Greiner and Levati 2005..g. .. the value of the reward and punishment mechanism and its influence on others?? behavior s are often not obvious to new users. Individuals do not make contribution in a vacuum. Asvanund et al. Robert. a significant difference between the two is the nature of digital goods. and T. Journal of Economic Perspectives 2 3 187-197. and K. Ekeh. Management Science 49 3 464?C477. Available at ssrn abstract=926915. As such. G achter. extrinsic. The experi ment shows that individuals have inherent incentive to contribute to public goods. 2007 . A. R. Hughes. Sobel. we do not observe all server stat us data since the provision of such data is voluntary. Ma. Las Vegas. A key feature of social punishme nt mechanisms is that they are initiated by indivi dual members of a society instead of orchestrated by any organization or enforced by any formal agreement. The results also provide support for all the hypotheses. therefore. Knowledge Management: An Evolutionary View of the Field. Familiarity. This proposition is. Wasko. we propose: H9: Experience ?C a contributor??s probability of providing priority services to other Louis Vuitton UK increases w ith her experience with the peer-to-peer network. However. 2000. Oppenheimer. Journal of Strategic Information Systems 9 2-3 155-173. Fehr and Gachter 2000a. Valacich. Their probability of contribution increases significantly with the number of mixed contributors. INFORMS Journal on Computing 20 1 100-111. Fehr and Gatcher 2000a . H4: Reputational incentives - A user??s probability of contribution increases after she receives special title in recognition of her contribution activities. 34 Krishnan. Casadesus-Masanell and Hervas-Drane 2007. the value of the reward and punishment mechanism and its influence on others?? behavior s are often not obvious to new users. Rockenbach and Milinsk i 2006 . The notion that individuals have incentive to punish non-cooperators in a social setting has been long observed in human so cieties. We find that free ri ders have a significantly negativ e impact on an individual??s contribution H1b . P. W hy share in peer-to-peer networks? Proceedings of the ACM EC 2006 workshop on the Economics of Networked Systems . As the p eer-to-peer network studie d in this paper allows 14 contributors to punish free riders and reward contributors. thus reducing free riding behavior and promoting cont ribution. Wasko and louis vuitton outlet 2000 find through surveys that individuals are motiv ated by indirect reciprocity in making contributions to online 6 communities. a user can easily determine the c ooperative environment in the network by observing the sharing level of other network users. Whinston. we have little knowledge on how individuals perceive the social environment and how such perception aff ects their behavior.. Sigmund. 59 1 63-80. B. M. Journal of Industrial Economics 50 2 197-234. Robert. D. P??nard. 2005. on average.
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• its server software allows contributors to punish free riders and reward fellow contributors using server priority setting. give access to other contributors only. 1999. 36 Tullberg. 2003. The sequential prisoner??s dilemma: evidence on reciprocation. 2005. a contributor does not expect Louis Vuitton UK Shop reciprocation from beneficiaries either because beneficiaries cannot afford to e. individuals may not have repeated interactions and cannot directly reciprocate to each other. E.. the resu lts show that individuals Louis vuitton uk more likely to use the reward and punishment mechanism to encourage contributi on and discourage free riding behavior after receiving special titles from the network H10 . Nowak and Sigm und Louis vuitton S. Table 3 reports the social influence of indirect reciprocity on the individual c ontribution. A. in peer-to-peer networks. H2: In-kind Indirect Reciprocit y ?C a user??s probability of contribution is less influenced by the number of pure contributors than by th e number of mixed contributors in a peer-to-peer network. 2001a. 2005. 2006. Cooperation and punishment in public goods experiments. in ma ny online environments. Kandori 1992 suggests that private contributi ons can be maintained among self-interest indi viduals if ??not only are deviators from the desired behavior punished. Kuk. but congestion costs are dependent on the congestion level and an indi vidual??s download needs. IROM-06-09 Indirect Reciprocity in Online Social Networks ?C A Longitudinal Analysis of Individual Contributions and Peer Enforcement in a Peer-to-Peer Music Sharing Network Bin Gu McCombs School of Business We thank Andres Hervas-Dra ne. H. decrease in value of shared conten ts due to wider availability. Lee. However. The game plays multiple rounds and players can observe each other??s level of contribution in the previous round. Extant research suggests that individuals reciprocate negative actions with negative actions Panchanathan and Boyd 2004. Peer-to-peer networks have increasingly become distribution and communication channels of digital files and a variety of mechanisms have been proposed to encourage file sharing and distribution. Fairness and retaliation: the economics of reciprocity. R. Handbook of Experimental Economics. The need for using the reward and punishment mechanism arises not only when a user observes an increase in free riders. H. Sproull. 2000. Management Science 32 11 1492?C1512. 2005. G. 2004. image score. 2006. each user downloads 22 music files on a given day with an average wait time of 13 minutes per file. By studying how individuals change server settings with the social environment. Han. The impact of free-riding on peer-to-peer networks. To account for contribution out Louis Vuitton Official self-interest. We conduct the analysis using a panel data by observing 103. Huang. R. We therefore propose: H6: Congestion - A user??s probability of cont ribution increases with wait time when the user has high download needs. A key feature of social punishme nt mechanisms is that they are initiated by indivi dual members of a society instead of orchestrated by any organization or enforced by any formal agreement. Parameswaran. J. Why should i sh are? Examining knowledge contribution in electronic networks of practice. in an ultimatum game. does not require obtaining benef its directly from the recipients. Management Science 52 7 1000-1014. A. In such cases. 1976. Many social factors exhibit positive feedback and. Once a contributor makes the contribution decision. and R. Slaughter. starting an avalanche across the network. and R. In particular. free riding can be discouraged by a tit-for-tat strategy. Second. A number of experimental studies show that individuals are willing to punish free riders and rewards contributors to encourage reciprocity on others even when the punishment is costly and bears no direct benefits Fehr and Gachter 2000a. 2007a . Organization Science 7 2 119?C135. B. Table 4 reports individual co ntributors?? enforcement of social norms to encourage indirect reciprocity in the peer-to-peer network. 2004. Our results indicate that users in peer-to-peer networks demo nstrate a rich set of dynamic behaviors consistent with indire ct reciprocity theory. the enforcement of social norms is inherent in human behavior and does not require extrinsic incentive to enforce. Hann. An important finding of this study is that individual contribution and peer enforcement change in response to network environments. Our analysis provides empirical evidences to show that indirect reciprocity is an important f actor for contribution. Ang. In such cases. Contributor characteristics influence indirect reciprocity in two ways. D. computer proficiency. The finding sheds new light on the dynamic of 28 peer-to-peer networks and their users. To develop an empirical hypothesis from the self-interest theory. the resu lts show that individuals are more likely to use the reward and punishment mechanism to encourage contributi on and discourage free riding behavior after receiving special titles from the network H10 . a key f eature of these networks is th at a contributor can determine whether. In many social environments. J. Foundations of human sociality: Economic experiments and et hnographic evidence from fifteen small-scale societies . The first set identifies the influence of social environments on individual contributions to the peer-to-peer network. image score. Stallaert. A. Second. The correlation between the two variables raises concerns about multicollinearity. Louis Vuitton UK Figure 1: Comparison of contribution level in repeated public good game without punishment mechanism against contribution level with punishment mechanis m obtained from Fehr and Gachter 2000b. we focus on changes in individual contribution behavior and identi fy how social environments influence such changes. Moreover. consistent with findings from prior lab experiments. Sigmund. Jeppesen. M. 1999. Users need to acquire the necessary technical kn owledge to activate the 18 reward and punishment mechanism. Our analysis indicates that indirect reciprocity could be a key motivating factor for contribut ion to peer-to-peer networks and has a significant influence on the social dynamics inside these networks. The Economic Journal 111 468 51-68. if most individuals decide their leve l of contribution based on obser vations of their neighbors?? contribution behavior. We control for thes e individual characterist ics using fixed effects . M. We therefore propose: H6: Congestion - A user??s probability of cont ribution increases with wait time when the user has high download needs. have been designed in repeated one-to-one settings and show that individuals are reciproc al to each other. Galit Shmueli. Stallaert.. We conclude the paper by identifying th e limitations and future research. The pr esence of indirect reciprocity in peer-to-peer networks. electronic mailing lists. While direct reciprocity often prevails in direct one-to-one economic exchanges. Peer-to-peer file sharing communities. Social exchange theory. First. give access to other contributors only. For example. R. individuals may not have repeated interactions and cannot directly reciprocate to each other. or pirated contents. and K. while individuals rarely have repeated one-to-one interactio ns in peer-to-peer networks. L.. we propose: H9: Experience ?C a contributor??s probability of providing priority services to other contributors increases w ith her experience with the peer-to-peer network. This corroborates the reciprocity theory that reciprocity is ba sed on contributors?? n eed Louis Vuitton Outlet Official intent. 2005. Available at ssrn abstract=926915. However. th ey do not capture the dynamic nature of so cial networks. 2 it i itContributionStatus t ?? ?? =++++ 1it it BX BZ 2 it i itServerStatus t ?? ?? =++++ 1it it ?? X ?? Z In the above models. Our analysis indicates that a network user significan tly increases her propensity to contribute after gaining special titles from the network. O. S. A. Second. The need for using such a reward and punishment mechanism is at the greatest when the network is overwhelmed with free riders and at the lowest when the network has a sufficient number of contributors. Slaughter. Team knowledge and coordination in geographically distributed software development. Spain. Butler.

  its server software allows contributors to punish free riders and reward fellow contributors using server priority setting. give access to other contributors only. 1999. 36 Tullberg. 2003. The sequential prisoner??s dilemma: evidence on reciprocation. 2005. a contributor does not expect Louis Vuitton UK Shop reciprocation from beneficiaries either because beneficiaries cannot afford to e. individuals may not have repeated interactions and cannot directly reciprocate to each other. E.. the resu lts show that individuals Louis vuitton uk more likely to use the reward and punishment mechanism to encourage contributi on and discourage free riding behavior after receiving special titles from the network H10 . Nowak and Sigm und Louis vuitton S. Table 3 reports the social influence of indirect reciprocity on the individual c ontribution. A. in peer-to-peer networks. H2: In-kind Indirect Reciprocit y ?C a user??s probability of contribution is less influenced by the number of pure contributors than by th e number of mixed contributors in a peer-to-peer network. 2001a. 2005. 2006. Cooperation and punishment in public goods experiments. in ma ny online environments. Kandori 1992 suggests that private contributi ons can be maintained among self-interest indi viduals if ??not only are deviators from the desired behavior punished. Kuk. but congestion costs are dependent on the congestion level and an indi vidual??s download needs. IROM-06-09 Indirect Reciprocity in Online Social Networks ?C A Longitudinal Analysis of Individual Contributions and Peer Enforcement in a Peer-to-Peer Music Sharing Network Bin Gu McCombs School of Business We thank Andres Hervas-Dra ne. H. decrease in value of shared conten ts due to wider availability. Lee. However. The game plays multiple rounds and players can observe each other??s level of contribution in the previous round. Extant research suggests that individuals reciprocate negative actions with negative actions Panchanathan and Boyd 2004. Peer-to-peer networks have increasingly become distribution and communication channels of digital files and a variety of mechanisms have been proposed to encourage file sharing and distribution. Fairness and retaliation: the economics of reciprocity. R. Handbook of Experimental Economics. The need for using the reward and punishment mechanism arises not only when a user observes an increase in free riders. H. Sproull. 2000. Management Science 32 11 1492?C1512. 2005. G. 2004. image score. 2006. each user downloads 22 music files on a given day with an average wait time of 13 minutes per file. By studying how individuals change server settings with the social environment. Han. The impact of free-riding on peer-to-peer networks. To account for contribution out Louis Vuitton Official self-interest. We conduct the analysis using a panel data by observing 103. Huang. R. We therefore propose: H6: Congestion - A user??s probability of cont ribution increases with wait time when the user has high download needs. A key feature of social punishme nt mechanisms is that they are initiated by indivi dual members of a society instead of orchestrated by any organization or enforced by any formal agreement. Parameswaran. J. Why should i sh are? Examining knowledge contribution in electronic networks of practice. in an ultimatum game. does not require obtaining benef its directly from the recipients. Management Science 52 7 1000-1014. A. In such cases. 1976. Many social factors exhibit positive feedback and. Once a contributor makes the contribution decision. and R. Slaughter. starting an avalanche across the network. and R. In particular. free riding can be discouraged by a tit-for-tat strategy. Second. A number of experimental studies show that individuals are willing to punish free riders and rewards contributors to encourage reciprocity on others even when the punishment is costly and bears no direct benefits Fehr and Gachter 2000a. 2007a . Organization Science 7 2 119?C135. B. Table 4 reports individual co ntributors?? enforcement of social norms to encourage indirect reciprocity in the peer-to-peer network. 2004. Our results indicate that users in peer-to-peer networks demo nstrate a rich set of dynamic behaviors consistent with indire ct reciprocity theory. the enforcement of social norms is inherent in human behavior and does not require extrinsic incentive to enforce. Hann. An important finding of this study is that individual contribution and peer enforcement change in response to network environments. Our analysis provides empirical evidences to show that indirect reciprocity is an important f actor for contribution. Ang. In such cases. Contributor characteristics influence indirect reciprocity in two ways. D. computer proficiency. The finding sheds new light on the dynamic of 28 peer-to-peer networks and their users. To develop an empirical hypothesis from the self-interest theory. the resu lts show that individuals are more likely to use the reward and punishment mechanism to encourage contributi on and discourage free riding behavior after receiving special titles from the network H10 . a key f eature of these networks is th at a contributor can determine whether. In many social environments. J. Foundations of human sociality: Economic experiments and et hnographic evidence from fifteen small-scale societies . The first set identifies the influence of social environments on individual contributions to the peer-to-peer network. image score. Stallaert. A. Second. The correlation between the two variables raises concerns about multicollinearity. Louis Vuitton UK Figure 1: Comparison of contribution level in repeated public good game without punishment mechanism against contribution level with punishment mechanis m obtained from Fehr and Gachter 2000b. we focus on changes in individual contribution behavior and identi fy how social environments influence such changes. Moreover. consistent with findings from prior lab experiments. Sigmund. Jeppesen. M. 1999. Users need to acquire the necessary technical kn owledge to activate the 18 reward and punishment mechanism. Our analysis indicates that indirect reciprocity could be a key motivating factor for contribut ion to peer-to-peer networks and has a significant influence on the social dynamics inside these networks. The Economic Journal 111 468 51-68. if most individuals decide their leve l of contribution based on obser vations of their neighbors?? contribution behavior. We control for thes e individual characterist ics using fixed effects . M. We therefore propose: H6: Congestion - A user??s probability of cont ribution increases with wait time when the user has high download needs. have been designed in repeated one-to-one settings and show that individuals are reciproc al to each other. Galit Shmueli. Stallaert.. We conclude the paper by identifying th e limitations and future research. The pr esence of indirect reciprocity in peer-to-peer networks. electronic mailing lists. While direct reciprocity often prevails in direct one-to-one economic exchanges. Peer-to-peer file sharing communities. Social exchange theory. First. give access to other contributors only. For example. R. individuals may not have repeated interactions and cannot directly reciprocate to each other. or pirated contents. and K. while individuals rarely have repeated one-to-one interactio ns in peer-to-peer networks. L.. we propose: H9: Experience ?C a contributor??s probability of providing priority services to other contributors increases w ith her experience with the peer-to-peer network. This corroborates the reciprocity theory that reciprocity is ba sed on contributors?? n eed Louis Vuitton Outlet Official intent. 2005. Available at ssrn abstract=926915. However. th ey do not capture the dynamic nature of so cial networks. 2 it i itContributionStatus t ?? ?? =++++ 1it it BX BZ 2 it i itServerStatus t ?? ?? =++++ 1it it ?? X ?? Z In the above models. Our analysis indicates that a network user significan tly increases her propensity to contribute after gaining special titles from the network. O. S. A. Second. The need for using such a reward and punishment mechanism is at the greatest when the network is overwhelmed with free riders and at the lowest when the network has a sufficient number of contributors. Slaughter. Team knowledge and coordination in geographically distributed software development. Spain. Butler.
• vor 23.12.2011 04:58
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• 1986b. Frederiksen. Gu. Hughes. Organization Science. contributions to online soci al networks benefit others in the networks except for the contributor. Louis Vuitton UK file sharing communities. contributors who both contribute to and download from the peer-to-peer network H1a Louis vuitton uk These concerns vary significantly across individuals but remain mostly unchanged over time for a given individual. Louis vuitton Science 49 2 160-178. the contributi on level decreases over time and gradually approaches zero. By studying how individuals change server settings with the social environment. M. Spain. Fehr. Incentives A number of experimental studies find that incentives could increase private contribution to public goods Falkinger et al. 2004. We find that an individual??s likelihood of contributions increases with the number of contri butors in the peer-to-p eer network but decreases with the number of free riders in the network. panel data enables us to control for individual heterogeneity. enjoyment in helping others. Proceedings of Multimedia Computing and Networking MMCN '02 . The kindness of strangers: The usefulness of electronic weak ties for technical advice. It woul d be useful in the future to identify the full distribution of reciprocity acros s individuals and study how the in teractions between individuals with different propensities of reciprocity influence contribution. Public Choice 86 1-2 117-135. We. First. the action of contributing often incurs significant costs for the contributor. Free-ri ding has also been reported Louis Vuitton Outlet UK a concern in studies on virtual professional networks. Galit Shmueli. The recipient of the helpful action could also return favors to a third-party. The analysis enriches our understa nding of underlying the motivation of contribution and provides new guidance to busine sses on peer-to-peer networks. R. The missing observations could create biases in our analysis if contributors that turn off their server status reporting features are systematically different from contributors that do not. but also a social norm that requires compliance. Indirect Reciprocity Reciprocity has been documented in a variety of economic experiments see Fehr and Cachter 2000a for a review . 2002. 2006. M. The efficient interaction of indirect reciprocity and costly punishment. While direct reciprocity often prevails in direct one-to-one economic exchanges.g. 30 Bapna. Indirect reciprocity arises in such a case when individuals respond in kind to a third-party or to the network in general. and M. Other Drivers for Contributions Besides concerns for indirect reciprocity. A theory of fairness. Sefton. 2005 . They show that individuals will punish others even if the enfor cement is costly and brings no benefits to the enforcer. Without la beling. S. on average. Espinosa. 1976. 2005. Second. unlike studies based on survey da ta. The new experiment reveals that individual contribution increases dramatically when peer punishment is enabled. consistent with findings from prior lab experiments. Louis vuitton handbags uk s who only contribute but never download signal that they do not need in-kind cont ributions from others and. we use the number of downloads requested in a given day as a control variable in our regression models. 1986b. The increase is consistent with the finding from economic experiments and Figure 1. and cooperation. Z. They do so through the setting of servers to discrimina te downloaders. Evolution of Indirect Reciprocity. Xia. Extant research has identified a variety of factors that motivate user contributions to online social networks. UIUC Working Paper . the analysis above indicates that indirect reciprocity is an important dynamic social force in peer-to-peer networks. 2005. Finally. While we do not observe these variables in our peer-to-peer network. 2005.. we consider our study complements to earlier studies that focus on identifying individual motivations but overlook th e dynamic nature of social networks. J. Sefton. Sloof. 2004. R. 2000b. reciprocation of music files provides little Louis Vuitton Cheap to contributors. S.V. Lab experiments show that the ability for individuals to punish free riders and reward contributors has a significant impact on contribution to public goods. Cunningham et al. The recipient of the helpful action could also return favors to a third-party. This indicates that cont ributors find fewer needs to motivate others?? to contribute when there are a sufficient number of contributors in the network.

  1986b. Frederiksen. Gu. Hughes. Organization Science. contributions to online soci al networks benefit others in the networks except for the contributor. Louis Vuitton UK file sharing communities. contributors who both contribute to and download from the peer-to-peer network H1a Louis vuitton uk These concerns vary significantly across individuals but remain mostly unchanged over time for a given individual. Louis vuitton Science 49 2 160-178. the contributi on level decreases over time and gradually approaches zero. By studying how individuals change server settings with the social environment. M. Spain. Fehr. Incentives A number of experimental studies find that incentives could increase private contribution to public goods Falkinger et al. 2004. We find that an individual??s likelihood of contributions increases with the number of contri butors in the peer-to-p eer network but decreases with the number of free riders in the network. panel data enables us to control for individual heterogeneity. enjoyment in helping others. Proceedings of Multimedia Computing and Networking MMCN '02 . The kindness of strangers: The usefulness of electronic weak ties for technical advice. It woul d be useful in the future to identify the full distribution of reciprocity acros s individuals and study how the in teractions between individuals with different propensities of reciprocity influence contribution. Public Choice 86 1-2 117-135. We. First. the action of contributing often incurs significant costs for the contributor. Free-ri ding has also been reported Louis Vuitton Outlet UK a concern in studies on virtual professional networks. Galit Shmueli. The recipient of the helpful action could also return favors to a third-party. The analysis enriches our understa nding of underlying the motivation of contribution and provides new guidance to busine sses on peer-to-peer networks. R. The missing observations could create biases in our analysis if contributors that turn off their server status reporting features are systematically different from contributors that do not. but also a social norm that requires compliance. Indirect Reciprocity Reciprocity has been documented in a variety of economic experiments see Fehr and Cachter 2000a for a review . 2002. 2006. M. The efficient interaction of indirect reciprocity and costly punishment. While direct reciprocity often prevails in direct one-to-one economic exchanges.g. 30 Bapna. Indirect reciprocity arises in such a case when individuals respond in kind to a third-party or to the network in general. and M. Other Drivers for Contributions Besides concerns for indirect reciprocity. A theory of fairness. Sefton. 2005 . They show that individuals will punish others even if the enfor cement is costly and brings no benefits to the enforcer. Without la beling. S. on average. Espinosa. 1976. 2005. Second. unlike studies based on survey da ta. The new experiment reveals that individual contribution increases dramatically when peer punishment is enabled. consistent with findings from prior lab experiments. Louis vuitton handbags uk s who only contribute but never download signal that they do not need in-kind cont ributions from others and. we use the number of downloads requested in a given day as a control variable in our regression models. 1986b. The increase is consistent with the finding from economic experiments and Figure 1. and cooperation. Z. They do so through the setting of servers to discrimina te downloaders. Evolution of Indirect Reciprocity. Xia. Extant research has identified a variety of factors that motivate user contributions to online social networks. UIUC Working Paper . the analysis above indicates that indirect reciprocity is an important dynamic social force in peer-to-peer networks. 2005. Finally. While we do not observe these variables in our peer-to-peer network. 2005.. we consider our study complements to earlier studies that focus on identifying individual motivations but overlook th e dynamic nature of social networks. J. Sefton. Sloof. 2004. R. 2000b. reciprocation of music files provides little Louis Vuitton Cheap to contributors. S.V. Lab experiments show that the ability for individuals to punish free riders and reward contributors has a significant impact on contribution to public goods. Cunningham et al. The recipient of the helpful action could also return favors to a third-party. This indicates that cont ributors find fewer needs to motivate others?? to contribute when there are a sufficient number of contributors in the network.
• vor 21.11.2011 08:04
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• Fashion risk-taking can end up a huge success or a serious embarrassment. For every new trend that really catches on (skinny jeans, leopard print), there are many more that bring on feelings of shame when looking at old photos (neon, parachute pants). Trends can be hit-or-miss, Black Ugg Boots Cheap Net where's the fun in not trying them at all?I enjoy taking the occasional fashion risk, and Black Ugg Boots Cheap it pays off. This season, I keep seeing oversized sweaters (let's call them fashion ponchos) in every store I go in. The type of poncho I'm talking about usually has short, shapeless sleeves and maybe a button in the middle to keep the whole thing from sliding off the shoulders. I brought a few to the fitting room and debated whether the poncho made me look boho-chic or like I was wearing a massive blanket around my shoulders.Eventually, I gave in a purchased a fashion poncho, much to the delight of my sister, who said I looked like a shepherd.Pulling off the fashion poncho can be tough - but it can be Clearance Uggs Outlet Online In Chestnut Hill, check out Fashion Forward Designer Resale for last season's designer ponchos and oversized sweaters. I have been seeing fashion ponchos on the runway for a while, but it hasn't broken into the mainstream until recently. Go with a simple silhouette of dark leggings and knee-high boots or classic flats. Nicole Miller in Manayunk carries lovely stretch pants that lengthen your legs and go great with oversized tops. If you make the bottom of your outfit look sophisticated enough, people will think your fashion poncho is cutting-edge and fashion-forward. Wear it with a pair of ill-fitting jeans and Ugg boots, and you risk being mocked for sartorial laziness. You may as well go out in your pajamas.Proper style is all about balance. Pair a super-trendy item like the fashion poncho with classic pieces from your wardrobe, and you can't go wrong. Besides, if you fail, you can toss out all photographic evidence of you in the offending item and tell your grandkids you never fell for trends.

  Fashion risk-taking can end up a huge success or a serious embarrassment. For every new trend that really catches on (skinny jeans, leopard print), there are many more that bring on feelings of shame when looking at old photos (neon, parachute pants). Trends can be hit-or-miss, Black Ugg Boots Cheap Net where's the fun in not trying them at all? I enjoy taking the occasional fashion risk, and Black Ugg Boots Cheap it pays off. This season, I keep seeing oversized sweaters (let's call them fashion ponchos) in every store I go in. The type of poncho I'm talking about usually has short, shapeless sleeves and maybe a button in the middle to keep the whole thing from sliding off the shoulders. I brought a few to the fitting room and debated whether the poncho made me look boho-chic or like I was wearing a massive blanket around my shoulders.Eventually, I gave in a purchased a fashion poncho, much to the delight of my sister, who said I looked like a shepherd. Pulling off the fashion poncho can be tough - but it can be Clearance Uggs Outlet Online In Chestnut Hill, check out Fashion Forward Designer Resale for last season's designer ponchos and oversized sweaters. I have been seeing fashion ponchos on the runway for a while, but it hasn't broken into the mainstream until recently. Go with a simple silhouette of dark leggings and knee-high boots or classic flats. Nicole Miller in Manayunk carries lovely stretch pants that lengthen your legs and go great with oversized tops. If you make the bottom of your outfit look sophisticated enough, people will think your fashion poncho is cutting-edge and fashion-forward. Wear it with a pair of ill-fitting jeans and Ugg boots, and you risk being mocked for sartorial laziness. You may as well go out in your pajamas. Proper style is all about balance. Pair a super-trendy item like the fashion poncho with classic pieces from your wardrobe, and you can't go wrong. Besides, if you fail, you can toss out all photographic evidence of you in the offending item and tell your grandkids you never fell for trends.
• vor 21.11.2011 08:28
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• finally unbearable to see HuangMei real open your mouth Cheap Uggs Online Sale US a sword from his mouth mans spewing out.The long sword mans about feet make to spread the spirit of the amazing power and in many bean sword mans surface of the size of the rune on circulation full of mysterious breath of of primitive simplicity.LinXuan counted the number of 49 way each sword of light that come out of a scattered-calms the all not less than ordinary yuan baby godsworn driven by top sponsors.LinXuan heart old monster face other horror and some pale legend is always nine times out of ten said they had not seen yuan late on each other shots the baby who just from the classics written is on income... How cheap ugg boots and some doubt it in general can now than those books is to meet that hasn't exaggerate place.However poison Jiao but the king don't care slightly deep voice came from the moncler jackets for women poison cloud "oh he had this level will want to progress but to how this the king?"Voice did not lie the poison cloud of the surge began a rumbling like HuangMei swoop in reality. A disease! "HuangMei real starts with a mans sword rushed to like wind storms immediately sword mans crazy to save the poison cloud sting.Just a contact the poison cloud was points plate thegoal of all the godsworn pits heart in a pleased after all you are Terran they still wanted HuangMei real win.But soon they aren't laughing because the poison cloud a surge after the attack but returned to Uggs Outlet Stores 2u in vain just... HuangMei real face a heavy this old demon than last saw even hard to deal with his hands up and take out another thing to the magic weapon., the two later monster began meeting is just wake a whirlwind of a series of other godsworn can't help have turned back afraid of being involved."Oh!"Suddenly a shrieks was introduced into the ear:...... HeHe old four you dare sneak attack me? "LinXuan looking back is a middle of the godsworn face such as Dan white paper his chest out the size of a fist blood hole.

  finally unbearable to see HuangMei real open your mouth Cheap Uggs Online Sale US a sword from his mouth mans spewing out. The long sword mans about feet make to spread the spirit of the amazing power and in many bean sword mans surface of the size of the rune on circulation full of mysterious breath of of primitive simplicity. LinXuan counted the number of 49 way each sword of light that come out of a scattered-calms the all not less than ordinary yuan baby godsworn driven by top sponsors. LinXuan heart old monster face other horror and some pale legend is always nine times out of ten said they had not seen yuan late on each other shots the baby who just from the classics written is on income... How cheap ugg boots and some doubt it in general can now than those books is to meet that hasn't exaggerate place. However poison Jiao but the king don't care slightly deep voice came from the moncler jackets for women poison cloud "oh he had this level will want to progress but to how this the king?" Voice did not lie the poison cloud of the surge began a rumbling like HuangMei swoop in reality. A disease! " HuangMei real starts with a mans sword rushed to like wind storms immediately sword mans crazy to save the poison cloud sting. Just a contact the poison cloud was points plate thegoal of all the godsworn pits heart in a pleased after all you are Terran they still wanted HuangMei real win. But soon they aren't laughing because the poison cloud a surge after the attack but returned to Uggs Outlet Stores 2u in vain just... HuangMei real face a heavy this old demon than last saw even hard to deal with his hands up and take out another thing to the magic weapon. , the two later monster began meeting is just wake a whirlwind of a series of other godsworn can't help have turned back afraid of being involved."Oh!" Suddenly a shrieks was introduced into the ear:...... HeHe old four you dare sneak attack me? " LinXuan looking back is a middle of the godsworn face such as Dan white paper his chest out the size of a fist blood hole.
• vor 21.11.2011 08:14
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• a short stature was mediocre the godsworn's surge of mana in his hand holding a drop of blood Bi eyes full of hate is the color of "zhang by oneself repaired for higher than me and spiral Pope in backing Chestnut Ugg Boots US behind a word" treacherous raised when I will endure things you do harmonious king Ugg Boots Style Hot Sale is the holy mountain you dare destroy rules?""Hum in order to be able to" vengeance is a smoke also don't care how much more do not have long been custom two elder destroyed." The diminutive godsworn cachinnation left hand one Yang that Bi into a hammer to cut the wu guang each other.ZhangXing godsworn throughout the chest is a mana also cannot raise brake up just watched as you fly wu guang."Hu eye to me down."The boy white deer somberly down two later old monster depending on the seal for nothing that he can only mountain rules YaoYaoYa endure can doesn't Discount Ugg Boots Outlet Online anything, dog can to cat here MuWu arrogant or elders."Be!"Several of the law enforcement that made of Dan to brake short the godsworn fly away.You are old four ready he and ZhangXing enemies like the moncler gaelle deep sea can fix for the power compared with each other than to come here and this is not something to trade.Seal the safety of the holy mountain is well known as an enemy here will relax timid, this is his police earn a brake want to annihilate the enemy.Even if that is again how together?See several law enforcement to fly to himself he not only do not hide it into a surprise size a rainbow ZhangXing godsworn like flew past.Several law enforcement to catch the wrath and newsletter but was quickly now not HeLaoSi face more and more red like to drop as bleeding.Terrible spirit force fluctuation!!!!!"Not he will choose from exploding!"

  a short stature was mediocre the godsworn's surge of mana in his hand holding a drop of blood Bi eyes full of hate is the color of "zhang by oneself repaired for higher than me and spiral Pope in backing Chestnut Ugg Boots US behind a word" treacherous raised when I will endure things you do harmonious king Ugg Boots Style Hot Sale is the holy mountain you dare destroy rules?" "Hum in order to be able to" vengeance is a smoke also don't care how much more do not have long been custom two elder destroyed." The diminutive godsworn cachinnation left hand one Yang that Bi into a hammer to cut the wu guang each other. ZhangXing godsworn throughout the chest is a mana also cannot raise brake up just watched as you fly wu guang."Hu eye to me down." The boy white deer somberly down two later old monster depending on the seal for nothing that he can only mountain rules YaoYaoYa endure can doesn't Discount Ugg Boots Outlet Online anything, dog can to cat here MuWu arrogant or elders."Be!" Several of the law enforcement that made of Dan to brake short the godsworn fly away. You are old four ready he and ZhangXing enemies like the moncler gaelle deep sea can fix for the power compared with each other than to come here and this is not something to trade. Seal the safety of the holy mountain is well known as an enemy here will relax timid, this is his police earn a brake want to annihilate the enemy. Even if that is again how together? See several law enforcement to fly to himself he not only do not hide it into a surprise size a rainbow ZhangXing godsworn like flew past. Several law enforcement to catch the wrath and newsletter but was quickly now not HeLaoSi face more and more red like to drop as bleeding. Terrible spirit force fluctuation!!!!!"Not he will choose from exploding!"
• vor 21.11.2011 08:33
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• around your neck doesn't bode well

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• vor 21.11.2011 08:27
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