This study has limitations. We were limited to inclusion in the study of the countries that had the resources and interest in being involved in this exercise. Considerable effort was expended to ensure that countries from every region worldwide were represented in the consortium, but we did not succeed in getting as much coverage as we would have liked; for example, French-speaking West Africa is not represented in the WMHS. This has meant that the current data do not represent every world region sufficiently.
