Air Pollution Increases Influenza Hospitalizations

Gregor Singer; Joshua Graff Zivin; Matthew Neidell; Nicholas Sanders

While our fixed effects can address many unobservable factors, there remain possible confounders in establishing a causal link between pollution exposure and influenza hospitalizations. Air quality could trigger health problems in sensitive populations (e.g. asthmatics) who would then go to the hospital, where they might be observed to have influenza. For this reason, our analysis focused on patients whose primary diagnosis is influenza and ignore occurrences of influenza in secondary diagnoses. We also repeat our analysis using two alternative measures: patients where influenza is the only diagnosis and patients where any diagnosis is influenza. Supplementary Appendix S.4 shows that our results are robust to either of these alternatives. We perform various falsification tests by repeating our analysis using health outcomes that should not correlate with air quality and health: diabetes mellitus with complications; urinary tract infections; skull and face fractures; and osteoarthritis (48). The result of a falsification test in Column (5), using the combined number of the above health outcomes, indicates a precise zero to the thousandth decimal place. We present estimates on each of these four falsification outcomes individually in Supplementary Appendix S.4 with similar results.