Geo-positioned surveys are imported into the mapping software Arc Map 9.3 (ERSI, Redlands, CA, USA). Point estimates of prevalence are categorized according to WHO prevalence thresholds used to denote treatment requirements, with an added category denoting zero prevalence: <0.1, 0.1-19.9, 20-49.9 and 50-100%.
The map of predicted infection risk is based on detailed statistical modelling, using an approach called Bayesian model-based geostatistics.
For further details, please see the supporting technical Information document:
Global Atlas of Helminth Infection (2010) Techincal information on developing Bayesian geostatistical models. London School of Hygiene and Tropical Medicine, UK.