UCLA

Distributions of the number of sexual partners reported in surveys show a pronounced skew, with most people having had one or no partners in the past year and a small fraction having had many1,2. Liljeros and colleagues3 infer from the results of a Swedish survey that there is a "scale-free" population distribution of sexual contacts, consistent with a preferential-attachment model3,4, in which “the rich get richer” and epidemics are driven by extremely promiscuous individuals. Here we reanalyse the data from Sweden and from other countries, using more appropriate statistical tools. Our findings support the conventional wisdom that epidemic thresholds exist in these populations, and indicate that current public-health strategies to reduce the spread of HIV and other sexually transmitted infections do not need to be radically refocused.