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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.

* [15] 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

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.

* [17] 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.



 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.

* [18] 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

 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             fax:+1-416-978-3963
  Updating history:

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