Study area, study region and study population
In our study, two similar terms "study area" and "study region" are used differently. The "study area" was defined as circles of radius 10 km from the MSW incinerators. To identify the study population that was defined as all live births, fetal deaths, and infant deaths occurred in the study area during a 2 year period of 1997 and 1998, we selected all the municipalities ("city", "ward","town" and "village") that were located within, or overlapped with the study area. The group of municipalities selected for each MSW incinerator was defined as the "study region" which is wider than the "study area" and is used as an adjustment factor to calculate the expected number of cases taking into account the regional difference of standardized mortality or incidence ratios. A total of 451 municipalities were selected.