Estimates of infection prevalence are derived from cross-sectional surveys conducted since 1980. Surveys are identified using a combination of approaches, including:
- Searches of electronic bibliographic databases
- Manual searches of local archives and libraries
- Direct contact with researchers
To ensure that only reliable surveys are included in the Global Atlas, pre-determined inclusion criteria are applied to information identified through searches. In particular, only cross-sectional prevalence surveys are included. Data are excluded if based on hospital or clinic surveys, post-intervention surveys, or surveys among sub-populations such as refugees, prisoners or nomads. Survey data are also excluded if prevalence was reported without a denominator, or if there were errors in the calculations presented. Where multiple surveys of the same location were carried out at different times, the most recent results were used.
Each source of information was reviewed and the data extracted into a standardized Microsoft Excel spreadsheet. Abstracted data included details on the source of the data, location of survey, characteristics of the surveyed population, survey methodology, number of individuals sampled and the number positive for each helminth species. Due to the diagnostic method typically used in field surveys, the two species of hookworm are not distinguished.
The geographical location – the longitude and latitude – of surveyed schools and communities is also determined to allow the mapping of data. This 'geo-positioning' is based on a variety of approaches and sources of information, using Microsoft Encarta Premium Edition 2007 and other online electronic gazetteers.