A SENSITIVITY ANALYSIS OF MORTALITY PM-10 ASSOCIATIONS IN LOS-ANGELES

Several recent studies have reported statistically significant and qua ntitatively similar associations between daily mortality and PM-10 or total suspended particulates (TSP). These results have raised question s of biological plausibility, as well as questions regarding the stati stical methods employed, which are relatively new and not widely under stood. This article evaluates the sensitivity of mortality/PM-10 resul ts to a range of statistical methods in a newly developed data set fro m Los Angeles county for the period 1985-1990. Data reported here incl ude total daily deaths (excluding accidents and suicides), 24-h averag e PM-10, daily 7-h maximum O-3 and carbon monoxide, maximum daily temp erature, and mean daily relative humidity. Analyses were limited to th e subset oi days on which PM-10 data were available (every sixth day). Several alternative methods for addressing each of four issues were e xplored in this data set These four issues were cyclic data variations , weather influences, other air pollutants, and the distribution of re siduals. The associations between mortality and PM-10 concentrations, measured as relative risks associated with a 100-mu g/m(3) increase in PM-10, were only mildly sensitive to the alternative statistical meth ods. In particular, no difference was observed between the results of ordinary least squares and Poisson models. We observed a relative risk of about 1.05, which is similar to, but somewhat smaller than, the mo rtality/PM-10 relative risks reported in recent studies. These new res ults add to the growing body of data suggesting that current levels of airborne particulate matter may contribute to excess deaths in the Un ited States.