Given that the HI values (or equivalent API values or categories) for Malaysia cover such a small range, it is clear that dose-response relationships for Malaysia can be derived only for the lower end of the pollution scales. Extrapolations of the Malaysian regression results to higher levels of pollution are thus more speculative. It is not possible to tell, from the available data, whether the dose-response relationship is linear for the full range of HI values or whether it is non-linear. In the absence of better data, a linear relationship is assumed in this chapter.