In the November 2003 issue of EHP, Liu et al. (2003) concluded that " relatively low concentrations of gaseous air pollutants are associated with adverse effects on birth outcomes. " Although this may be true from a purely statistical sense, there appear to be limitations of this research that suggest cautious interpretation of the findings. Liu et al. (2003) evaluated individual-level birth ce...

In the November 2003 issue of EHP, Liu et al. (2003) concluded that " relatively low concentrations of gaseous air pollutants are associated with adverse effects on birth outcomes. " Although this may be true from a purely statistical sense, there appear to be limitations of this research that suggest cautious interpretation of the findings. Liu et al. (2003) evaluated individual-level birth ce...

This paper reviews multilevel and conventional models for the analysis of ecologic (group, aggregate) data. It emphasizes the non-separability of contextual (group-level) effects and individual-level effects that arises from the multilevel structure of the underlying effects. Contrary to common misperceptions, this problem afflicts ecologic studies in which the sole objective is to estimate con...

In the November 2003 issue of EHP, Liu et al. (2003) concluded that " relatively low concentrations of gaseous air pollutants are associated with adverse effects on birth outcomes. " Although this may be true from a purely statistical sense, there appear to be limitations of this research that suggest cautious interpretation of the findings. Liu et al. (2003) evaluated individual-level birth ce...

In the November 2003 issue of EHP, Liu et al. (2003) concluded that " relatively low concentrations of gaseous air pollutants are associated with adverse effects on birth outcomes. " Although this may be true from a purely statistical sense, there appear to be limitations of this research that suggest cautious interpretation of the findings. Liu et al. (2003) evaluated individual-level birth ce...

In the November 2003 issue of EHP, Liu et al. (2003) concluded that " relatively low concentrations of gaseous air pollutants are associated with adverse effects on birth outcomes. " Although this may be true from a purely statistical sense, there appear to be limitations of this research that suggest cautious interpretation of the findings. Liu et al. (2003) evaluated individual-level birth ce...

In the November 2003 issue of EHP, Liu et al. (2003) concluded that " relatively low concentrations of gaseous air pollutants are associated with adverse effects on birth outcomes. " Although this may be true from a purely statistical sense, there appear to be limitations of this research that suggest cautious interpretation of the findings. Liu et al. (2003) evaluated individual-level birth ce...

In the November 2003 issue of EHP, Liu et al. (2003) concluded that " relatively low concentrations of gaseous air pollutants are associated with adverse effects on birth outcomes. " Although this may be true from a purely statistical sense, there appear to be limitations of this research that suggest cautious interpretation of the findings. Liu et al. (2003) evaluated individual-level birth ce...

This paper reviews some methodological aspects of ecologic studies of human health, with emphasis on investigations of environmental quality. A recent census of Canadian and U.S. data sets potentially suitable for this type of study is summarized. It is concluded that despite the considerable utility of the ecologic design for this purpose, substantial practical difficulties are common in their...