Figure 4: Assortativity and the probability of extinction. The probability of extinction in a fully susceptible population given a single adult or child index case is measured as a function of , the proportion of within-group mixing. The next-generation matrix, parameterized by Fraser et al. [6] with the dominant eigenvalue , is rescaled by multiplying each entry with where is set to be 1.2, 1.4 and 1.6, respectively.