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. 2018 Aug 2;18:82. doi: 10.1186/s12874-018-0541-7

Fig. 1.

Fig. 1

Model structure of a hypothetical chronic sexually transmitted infection. The arrows represent the possible transitions. These are governed by the parameters ϕr,s with indices r,sS representing origin and target states, respectively. The replenishment of the pool of susceptibles by newborns proceeds at a rate χ