Fig. 3: Posterior probability of the need for population-level trachoma interventions using seroconversion rate.

Posterior probability of programmatic ‘Action not needed‘ versus ‘Action needed‘ categories along a range of seroconversion rates (SCRs) among 1–5-year-olds calculated using a two-component Bayesian mixture model (Methods). A Posterior functions assume moderately informative prior probabilities of 80% ‘Action not needed‘ and 20% ‘Action needed‘. In principle, the posterior probability functions allow for the selection of thresholds to inform decisions based on serological surveys with a desired level of certainty. For example, at a ≥ 90% level of certainty, SCR of ≤2.2 per 100 person-years corresponds to a posterior probability of ‘Action not needed‘ and a SCR of ≥4.5 corresponds to a posterior probability of ‘Action needed‘. SCR values > 2.2 and <4.5 per 100 person-years may require additional information to inform programmatic action. B Posterior functions assume an uninformative prior of 50% ‘Action not needed‘ and 50% ‘Action needed‘. Sensitivity analyses in Supplementary Fig. 4 demonstrate that posterior probabilities are insensitive to the prior assumptions.