Estimating long-term pollution exposure effects through inverse probability weighting methods with Cox proportional hazards models

Joshua D Higbee; Jacob S Lefler; Richard T Burnett; Majid Ezzati; Julian D Marshall; Sun-Young Kim; Matthew Bechle; Allen L Robinson; C Arden Pope 3rd

doi:10.1097/EE9.0000000000000085

Estimating long-term pollution exposure effects through inverse probability weighting methods with Cox proportional hazards models

Environ Epidemiol. 2020 Apr 9;4(2):e085. doi: 10.1097/EE9.0000000000000085. eCollection 2020 Apr.

Authors

Joshua D Higbee¹, Jacob S Lefler², Richard T Burnett³, Majid Ezzati⁴, Julian D Marshall⁵, Sun-Young Kim⁶, Matthew Bechle⁵, Allen L Robinson⁷, C Arden Pope 3rd⁸

Affiliations

¹ Department of Economics, University of Chicago, Chicago, Illinois.
² Department of Agricultural and Resource Economics, University of California - Berkeley, Berkeley, California.
³ Health Canada, Ottawa, Ontario, Canada.
⁴ MRC-PHE Centre for Environment and Health, School of Public Health, Imperial College London, London, United Kingdom.
⁵ Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington.
⁶ Department of Cancer Control and Population Health, Graduate School of Cancer Science and Policy, National Cancer Center, Goyang-si, Gyeonggi-do, Korea.
⁷ Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, Pennsylvania.
⁸ Department of Economics, Brigham Young University, Provo, Utah.

Abstract

Background: Fine particulate matter (PM_2.5) is associated with negative health outcomes in both the short and long term. However, the cohort studies that have produced many of the estimates of long-term exposure associations may fail to account for selection bias in pollution exposure as well as covariate imbalance in the study population; therefore, causal modeling techniques may be beneficial.

Methods: Twenty-nine years of data from the National Health Interview Survey (NHIS) was compiled and linked to modeled annual average outdoor PM_2.5 concentration and restricted-use mortality data. A series of Cox proportional hazards models, adjusted using inverse probability weights, yielded causal risk estimates of long-term exposure to ambient PM_2.5 on all-cause and cardiopulmonary mortality.

Results: Covariate-adjusted estimated relative risks per 10 μg/m³ increase in PM_2.5 exposure were estimated to be 1.117 (1.083, 1.152) for all-cause mortality and 1.232 (1.174, 1.292) for cardiopulmonary mortality. Inverse probability weighted Cox models provide relatively consistent and robust estimates similar to those in the unweighted baseline multivariate Cox model, though they have marginally lower point estimates and higher standard errors.

Conclusions: These results provide evidence that long-term exposure to PM_2.5 contributes to increased mortality risk in US adults and that the estimated effects are generally robust to modeling choices. The size and robustness of estimated associations highlight the importance of clean air as a matter of public health. Estimated confounding due to measured covariates appears minimal in the NHIS cohort, and various distributional assumptions have little bearing on the magnitude or standard errors of estimated causal associations.

Keywords: Fine particulate matter; Inverse probability of treatment weighting; Mortality; National Health Interview Survey; Pollution.

Abstract

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