Speaker: Joshua Warren, PhD, Associate Professor, the Department of Biostatistics, Yale School of Public Health.

Bio: Joshua Warren is an associate professor in the Department of Biostatistics at the Yale School of Public Health. He received his Ph.D. in statistics from North Carolina State University in 2011. Dr. Warren’s research focuses on statistical methods in public health with an emphasis on environmental health problems. Much of his work involves introducing spatial and spatiotemporal models in the Bayesian setting to learn more about associations between environmental exposures, such as air pollution, and various health outcomes including preterm birth, low birth weight, and congenital anomalies. He also has interest in developing and applying spatiotemporal models in collaborative settings such as infectious disease epidemiology, geography, nutrition, and glaucoma research. His theoretical and methodological interests include multiple topics in spatial/spatiotemporal modeling and Bayesian nonparametrics.

Abstract: Understanding the role of time-varying pollution mixtures on human health is critical as people are simultaneously exposed to multiple pollutants during their lives. For vulnerable sub-populations who have well-defined exposure periods (e.g., pregnant women), questions regarding critical windows of exposure to these mixtures are important for mitigating harm. We extend Critical Window Variable Selection (CWVS) to the multipollutant setting by introducing CWVS for Mixtures (CWVSmix), a hierarchical Bayesian method that combines smoothed variable selection and correlated Dirichlet-distributed parameters to (i) identify critical windows of exposure to mixtures of time-varying pollutants, (ii) estimate the time-varying relative importance of each individual pollutant within the mixture, and (iii) quantify the impact of the mixtures on health. Through simulation study, we show that CWVSmix outperforms competing methods in each of these categories. We use these approaches to investigate the impact of exposure to 12 gas and particulate ambient air pollutants on the risk of stillbirth in New Jersey, 2005-2014. We find consistent elevated risk in gestational weeks 16-17 for non-Hispanic Black mothers, with pollution mixtures dominated by nitrogen oxides, carbon monoxide, nitrogen dioxide, and nitrate (week 16), and ammonium, nitrate (week 17). The method is available in the R package CWVSmix.

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