Air Pollution Increases Influenza Hospitalizations

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

Supplementary Appendix S.4 ex-plores heterogeneity and conducts further sensitivity analysis and robustness checks. Our estimates are stable across gender and age groups. We find suggestively larger effects for blacks and Hispanics, but the estimates are not statistically different from those for whites. We show robustness to (i) different weather controls, (ii) additional fixed effects, (iii) multilevel clustering of standard errors, (iv) different winsorization and interpolation of the raw AQI data, (v) including out-state patients at hospitals, (vi) focusing on states with a long time series only, (vii) using missing values instead of zeros for county-months with no hospital admissions, and (viii) using a linear ordinary least squares instead of a Poisson Pseudo-Maximum Likelihood estimator. We also show the effect of air pollution on outpatient hospitalization is larger than for inpatient hospitalizations, consistent with the notion that emergency department encounters are more frequent (but also less severe) than those requiring admission to the hospital.