Figure 3

Typical time-series of annual incidence specified by the temporal volatility model. The dashed line is the expected incidence (per 1,000 individuals per annum (p.a.)) and the horizontal bars are the observed incidence. The left panel illustrates an "endemic" region of high parasite rate. The incidence in any month is close to the long-term mean, which is relatively high. The right panel shows an "epidemic" region of low parasite rate. The incidence in most months is well below the long-term mean, but occasionally is much greater. The long-term mean in the low parasite rate region is lower than in the high parasite rate region but monthly incidence in the former can occasionally exceed that in the latter.