Scale-free networks and sexually transmitted diseases: a description of observed patterns of sexual contacts in Britain and Zimbabwe
Schneeberger, A.; Mercer, C.H.; Gregson, S.A.J.; Ferguson, N.M.; Nyamukapa, C.A.; Anderson, R.M.; Johnson, A.M.; Garnett, G.P.
Sexually Transmitted Diseases 31(6): 380-387
2004
ISSN/ISBN: 0148-5717 PMID: 15167650 DOI: 10.1097/00007435-200406000-00012Document Number: 251372
Background: 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. Objective: 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. Study Design: 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 I from rural Zimbabwe. Results: 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). Conclusions: A scale-free network approach provides a reasonable description of distributions of reported numbers of sexual partners.