Relationship between parasite rate and incidence. Left: the posterior distribution of expected population-wide incidence (per 1000 individuals per annum (p.a.)) against prevalence. This relationship would describe the observed incidence if surveillance were conducted for a very long time. Right: the predictive distribution of actual population-wide incidence per 1000 individuals in any given year. The right-hand panels take temporal volatility into account, therefore, whereas the left-hand panels average it out. The top row shows the Africa+ region (n = 25) and the bottom the CSE Asia and the Americas regions combined (n = 116). The data points are the red dots, the black line is the median and the 0.25, 0.5 and 0.95 credible intervals centred on the median are shown in shades of progressively lighter grey.