***** To join INSNA, visit http://www.insna.org ***** Patient Referral Patterns and the Spread of Hospital-Acquired Infections through National Health Care Networks , PLoS Comput Biol Summary: The prevalence of hospital acquired infections is widely believed to reflect the quality of health care in individual hospitals, and is therefore often used as a benchmark. Intuitively, the idea is that infections spread more easily in hospitals with a poor quality of health care. This assumes that the rate at which admitted patients introduce new infections is the same for all hospitals. In this article, we show that this assumption is unlikely to be correct. Using national data on patient admissions, we are able to reconstruct the entire hospital network consisting of patients referred between hospitals. This network reveals that university hospitals admit more patients that recently stayed in other hospitals. Consequently, they are more likely to admit patients that still carry pathogens acquired during their previous hospital stay. Therefore, the prevalence of infections does not only reflect the quality of health care but also the connectedness to hospitals from which patients are referred. This phenomenon is missed at the single hospital level; our study is the first to address the connectedness between hospitals in explaining the prevalence of hospital acquired infections. Our findings imply that interventions should focus on hospitals that are central in the network of patient referrals. *  Patient Referral Patterns and the Spread of Hospital-Acquired Infections through National Health Care Networks, Tjibbe Donker, Jacco Wallinga, Hajo Grundmann, 2010/03/19, DOI: 10.1371/journal.pcbi.1000715, PLoS Comput Biol 6(3): e1000715 http://dx.doi.org/10.1371/journal.pcbi.1000715 ---------------------- Cooperation , PLoS Comput Biol Summary: Cooperation is a fundamental and widespread phenomenon in nature, yet explaining the evolution of cooperation is difficult. Natural selection typically favors individuals that maximize their own reproduction, so how is it that many diverse organisms, from bacteria to humans, have evolved to help others at a cost to themselves? Research has shown that cooperation can most readily evolve when cooperative individuals preferentially help each other, but this leaves open another critical question: How do cooperators achieve selective interaction with one another? We focus on this question in the context of unicellular organisms, such as bacteria, which exhibit simple forms of cooperation that play roles in nutrient acquisition and pathogenesis. We use a realistic simulation framework to model large cell groups, and observe that cell lines can spontaneously segregate from each other in space as the group expands. Finally, we demonstrate that lineage segregation allows cooperative cell types to preferentially benefit each other, thereby favoring the evolution of cooperation. *  Emergence of Spatial Structure in Cell Groups and the Evolution of Cooperation, Nadell CD, Foster KR, Xavier JB, 2010/03/19, DOI: 10.1371/journal.pcbi.1000716, PLoS Comput Biol 6(3): e1000716.  http://dx.doi.org/10.1371/journal.pcbi.1000716 -------------------------- Markets, Religion, Community Size, and the Evolution of Fairness and Punishment , Science Excerpt: Large-scale societies in which strangers regularly engage in mutually beneficial transactions are puzzling. The evolutionary mechanisms associated with kinship and reciprocity, which underpin much of primate sociality, do not readily extend to large unrelated groups. Theory suggests that the evolution of such societies may have required norms and institutions that sustain fairness in ephemeral exchanges. If that is true, then engagement in larger-scale institutions, such as markets and world religions, should be associated with greater fairness, and larger communities should punish unfairness more. Using three behavioral experiments administered across 15 diverse populations, we show that market integration (measured as the percentage of purchased calories) positively covaries with fairness while community size positively covaries with punishment. *  Markets, Religion, Community Size, and the Evolution of Fairness and Punishment, Joseph Henrich, et al., 2010/03/19, DOI: 10.1126/science. 1182238, Science Vol. 327. no. 5972, pp. 1480 - 1484  http://dx.doi.org/10.1126/science.1182238 Barry Wellman _______________________________________________________________________ S.D. Clark Professor of Sociology, FRSC NetLab Director Department of Sociology 725 Spadina Avenue, Room 388 University of Toronto Toronto Canada M5S 2J4 twitter:barrywellman http://www.chass.utoronto.ca/~wellman fax:+1-416-978-3963 Updating history: http://chass.utoronto.ca/oldnew/cybertimes.php _______________________________________________________________________ _____________________________________________________________________ SOCNET is a service of INSNA, the professional association for social network researchers (http://www.insna.org). To unsubscribe, send an email message to [log in to unmask] containing the line UNSUBSCRIBE SOCNET in the body of the message.