Goods Movement Actions Improved Air Quality and Health Outcomes among California Medicaid Enrollees
Ying-Ying Meng1, Dahai Yue1, Jason G. Su2, Michael Jerrett1, Xiao Chen1, John Molitor3
1University of California at Los Angeles, Los Angeles, CA, USA; 2University of California at Berkeley, Berkeley, CA, USA; 3Oregon State University, Corvallis, OR, USA
Background: This project aims to examine the impact of the “Emissions Reduction Plan for Ports and Goods Movement” of the California Air Resources Board (CARB) in 2006 on reductions in ambient air pollution and subsequent improvements in health outcomes among Medicaid fee-for-service (FFS) beneficiaries in 10 counties in California. Specifically, we examined whether air pollution reduction actions resulted in decreases in emergency department (ED) visits and hospitalizations among enrollees with chronic conditions.
Methods: The study areas were grouped into goods movement corridors (GMCs) as locations within 500 m of truck-permitted freeways and ports; non-goods movement corridors (NGMCs) as locations within 500 m of truck-prohibited freeways or 300 m of a connecting roadway, and controls (CTRLs). We created annual air pollution surfaces for NO2, PM2.5 and ozone across California at a spatial resolution of 30 m, then assigned them to enrollees’ home addresses. We used a retrospective cohort of 23,000 adults with six years of data (September 1, 2004 to August 31, 2010). We analyzed data using a multilevel generalized linear model with negative binomial distribution and random intercepts for enrollees. We estimated the predicted outcomes for enrollees in GMC with and without policy by using the control group as the counterfactual. To facilitate interpretation, we calculated difference-in-differences (DD) estimates in the first-, second- and third-year after the policy intervention, respectively. To verify the parallel assumption, we also visualized the empirical time trend and tested the differential trends statistically.
Results: We observed significant reductions in pollutant exposures for enrollees in 10 counties with the enrollees in GMCs experiencing the greatest reduction from the pre- to post-policy periods. Furthermore, we observed statistically significant reductions in ED visits in the study population in post-policy years. For instance, the number of ED visits among those with asthma living in GMCs significantly decreased comparing with those living in CTRLs in the second year (DD=-0.08, p<0.01) and third year (DD=-0.08, p<0.01) post-policy. ED visits for those with chronic obstructive pulmonary disease (COPD) were reduced in post-policy years but the policy effects were only found to be statistically significant in the third post-policy year (DD=-0.09, p<0.005).
Conclusions: Our findings add to empirical evidence that air pollution control actions reduce pollution exposures; and lead to health outcome improvements among people with chronic conditions. Our investigation also contributes to scientific methods for accountability studies assessing the health effects of long-term, large scale, and complex regulatory actions with routinely collected data, such as medical claims data.
Poster by Meng et al., 2019 HEI Annual Conference