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Sex Transm Dis. 2004 Jun;31(6):380-7.

Scale-free networks and sexually transmitted diseases: a description of observed patterns of sexual contacts in Britain and Zimbabwe.

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Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial College, London, UK.



Sexually transmitted infections spread through a network of contacts created by the formation of sexual partnerships. In physics, networks have been characterized as "scale-free" if they follow a power law with an exponent between 2 and 3.


The objective of this study was to test statistically whether distributions of numbers of sexual partners reported from different populations are well described by power laws.


Power laws and an exponential null model are fitted by maximum likelihood techniques to reported distributions of numbers of partners. Data are taken from 4 population-based surveys, 3 from Britain and 1 from rural Zimbabwe.


The networks can be described by power laws over a number of orders of magnitude. In addition, the derived exponents differ significantly and meaningfully, with an "accelerating network" formed between men who have sex with men (MSM).


A scale-free network approach provides a reasonable description of distributions of reported numbers of sexual partners.

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