As a consequence of the uncertainties in this global assessment, its quan- titative results cannot be confidently extrapolated to smaller geographic areas, such as specific countries or cities. The methods for estimation of exposure and extrapolation of concentration-response functions were devel- oped specifically for estimating burdens for large geographic regions, often in the absence of essential data on exposure and response. Where better data exist, as they currently do in some parts of the world, they should of course be used. Future estimates of the global burden of disease due to outdoor air pollution would benefit from both additional research and methods development. There is a critical need for better.
