TY - JOUR
T1 - Does weather confound or modify the association of particulate air pollution with mortality?
T2 - An analysis of the Philadelphia data, 1973-1980
AU - Samet, Jonathan
AU - Zeger, Scott
AU - Kelsall, Julia
AU - Xu, Jing
AU - Kalkstein, Laurence
N1 - Funding Information:
1Research described in this article was conducted under contract to the Health Effects Institute, an organization jointly funded by the Environmental Protection Agency (EPA Assistance Award R824835) and automotive manufacturers. The contents of this article do not necessarily re¯ect the views of the Health Effects Institute, nor do they necessarily re¯ect the views and policies of the Environmental Protection Agency or motor vehicle or engine manufacturers. Any studies cited in this paper that involve humans were conducted in accordance with national and institutional guidelines for the protection of human subjects.
PY - 1998/4
Y1 - 1998/4
N2 - Because weather has the potential to confound or modify the pollution- mortality relationship, researchers have developed several approaches for controlling it in estimating the independent effect of air pollution on mortality. This report considers the consequences of using alternative approaches to controlling for weather and explores modification of air pollution effects by weather, as weather patterns could plausibly alter air pollution's effect on health. We analyzed 1973-1980 total mortality data for Philadelphia using four weather models and compared estimates of the effects of TSP and SO2 on mortality using a Poisson regression model. Two synoptic categories developed by Kalkstein were selected - the Temporal Synoptic Index (TSI) and the Spatial Synoptic Classification (SSC) - and compared with (1) descriptive models developed by Schwartz and Dockery (S-D); and (2) LOESS, a nonparametric function of the previous day's temperature and dew point. We considered model fit using Akaike's Information Criterion (AIC) and changes in the estimated effects of TSP and SO2. In the full-year analysis, S-D is better than LOESS at prediciting mortality, and S-D and LOESS are better than TSI, as measured by AIC. When TSP or SO2 was fit alone, the results were qualitatively similar, regardless of how weather was controlled; when TSP and SO2 were fit simultaneously, the S-D and LOESS models give qualitatively different results than TSI, which attributes more of the pollution effect to SO2 than to TSP. Model fit is substantially poorer with TSI. This pattern was repeated in analyses of summer and winter months, which included SSC. In summary, using synoptic weather categories in regression models does not meaningfully change the association between mortality and air pollution indexes. We also found little evidence that weather conditions modified the effect of pollution, regardless of the approach used to represent weather.
AB - Because weather has the potential to confound or modify the pollution- mortality relationship, researchers have developed several approaches for controlling it in estimating the independent effect of air pollution on mortality. This report considers the consequences of using alternative approaches to controlling for weather and explores modification of air pollution effects by weather, as weather patterns could plausibly alter air pollution's effect on health. We analyzed 1973-1980 total mortality data for Philadelphia using four weather models and compared estimates of the effects of TSP and SO2 on mortality using a Poisson regression model. Two synoptic categories developed by Kalkstein were selected - the Temporal Synoptic Index (TSI) and the Spatial Synoptic Classification (SSC) - and compared with (1) descriptive models developed by Schwartz and Dockery (S-D); and (2) LOESS, a nonparametric function of the previous day's temperature and dew point. We considered model fit using Akaike's Information Criterion (AIC) and changes in the estimated effects of TSP and SO2. In the full-year analysis, S-D is better than LOESS at prediciting mortality, and S-D and LOESS are better than TSI, as measured by AIC. When TSP or SO2 was fit alone, the results were qualitatively similar, regardless of how weather was controlled; when TSP and SO2 were fit simultaneously, the S-D and LOESS models give qualitatively different results than TSI, which attributes more of the pollution effect to SO2 than to TSP. Model fit is substantially poorer with TSI. This pattern was repeated in analyses of summer and winter months, which included SSC. In summary, using synoptic weather categories in regression models does not meaningfully change the association between mortality and air pollution indexes. We also found little evidence that weather conditions modified the effect of pollution, regardless of the approach used to represent weather.
KW - Daily mortality
KW - Model fit
KW - Particulate air pollution
KW - Synoptic approach
KW - Weather models
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U2 - 10.1006/enrs.1997.3821
DO - 10.1006/enrs.1997.3821
M3 - Article
C2 - 9593623
AN - SCOPUS:0032054358
SN - 0013-9351
VL - 77
SP - 9
EP - 19
JO - Environmental research
JF - Environmental research
IS - 1
ER -