Carter and Mendis1 provide some welcome clarity to their methods to estimate Plasmodium falciparum morbidity in re- gions of the world outside of Africa.2 The entry point to their estimation of morbid burdens is malaria-specific deaths re- ported by national governments. These reflect national mor- tality statistics generated through civil registration systems that allow for cause of death reporting and invariably only represent deaths that occur in health facilities able to diag- nose malaria. In many resource-poor settings, these recorded events represent only a small fraction of the universe of mor- tality in a given community.3,4 To redress this, Carter and Mendis have adjusted for under-reporting rates. How this was achieved in the absence of comparisons with prospective de- mographic surveillance system data remains unclear. To illus- trate the problem inherent in any method using national vital event reporting systems, one need look no further than the national malaria mortality data reported in the WHO's 2005 World Malaria Report.5 In 2003, mortality data are available for only 29 of 49 countries at risk of malaria transmission outside of Africa; a total of 5,865 malaria deaths were re- ported; 42% were reported from a single country—Myanmar. Sri Lanka reported only two malaria deaths. Estimates of reporting coverage were provided for only four countries. Despite this uncertainty, Carter and Mendis apply a series of country-specific case-fatality estimates derived from a com- bination of expert consultation, personal opinion, and unref- erenced literature. This step in their calculations is critically dependent upon reliable estimates of the true incidence of malaria morbidity and mortality. The probability of a clinical event resulting in death is the subject of fierce scientific de- bate surrounding the relationships between acquired func- tional immunity,6,7 access to care,8 and the role of cross- species protection9,10 versus disease outcome. Outside Africa there are only a handful of carefully conducted studies of P. falciparum clinical incidence and mortality undertaken using active-case detection methods within well-characterized populations subjected to prospective demographic surveil- lance with cause-of-death attribution of all fatal events.11,12 Empirical evidence upon which to reliably model global variations in case-fatality is largely absent, and therefore es- timating subregional case-fatalities must be the subject of guesswork and speculation. The area of largest uncertainty, for which Carter and Men- dis fail to define in their methodology, is the denominator. The numbers of people living under differing levels of P. falciparum transmission risk is arguably the single largest de- terminant of precision for morbidity and mortality burdens definitions globally.13 Our approach to defining population- attributable risks involved a conservative downregulation of historically mapped global malaria endemicity distributions.14 We acknowledged that these must be improved during future iterations of the estimation of malaria burden worldwide. In 2005, we started to extend our earlier work on transmission mapping to other regions of the world using empirical para- site rate survey data within spatially explicit models of dom- inant vector species P. falciparum transmission globally—the Malaria Atlas Project (MAP). These should provide a more robust and dynamic approach to defining the denominators for future disease burden estimations. This is particularly im- portant for the rapidly changing ecological context of the Western Pacific and Southeast Asian regions, which are home to some of the most densely populated malarious areas on the planet.13,14