Improvements in Air Quality and Health Outcomes among California Medicaid Enrollees Due to Goods Movement Actions
Ying-Ying Meng1, Jason G. Su2, Michael Jerrett3, Xiao Chen1, John Molitor4, Dahai Yue1
1 UCLA Center for Health Policy Research, University of California at Los Angeles (UCLA), Los Angeles, California, United States; 2 Division of Environmental Health Sciences, School of Public Health, University of California at Berkeley, Berkeley, California, United States; 3 Department of Environmental Health Sciences, Fielding School of Public Health, UCLA, Los Angeles, California, United States; 4 School of Biological and Population Health Sciences, Oregon State University, Corvallis, Oregon, United States
Background and Objectives: This 2-Phased project aims to examine reductions in ambient air pollution after the implementation of the “Emissions Reduction Plan for Ports and Goods Movement” by the California Air Resources Board (CARB) in 2006 and subsequent improvements in health outcomes of Medicaid fee-for-service (FFS) beneficiaries in 10 counties in California. Specifically, we examined whether air pollution reductions resulted in reductions in emergency department (ED) visits and hospitalizations among enrollees with chronic conditions.
Methods: We created annual air pollution surfaces across California at a spatial resolution of 30m. 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 control areas (CTRLs). In Phase II, exposures were assigned to enrollees’ home addresses. We used a retrospective cohort of 23,000 adult with six years of continuous enrollment (September 1, 2004 to August 31, 2010). Multilevel negative binomial regression models with random intercept for controlling within individual correlation were used to examine temporal changes of ED visits or hospitalizations by comparing GMCs with CTRLs. Based on the parallel assumption, difference in difference (DD) analyses have been conducted for assessing the causal impact of policy on reduction of air pollution, as well as for the causal impact of the reduction of air pollution on improvements in health outcomes.
Results: We observed significant reductions in pollutant exposures for enrollees living in 10 counties with the enrollees in GMCs experienced the greatest reduction from the pre- to the post-policy periods for NO2 and PM2.5 using the annual air pollution surfaces. We also observed that the number of ED visits among those with asthma living in GMCs were significantly lower (DD=-0.16, p<0.05) compared with those living in CTRLs. The ED visits for those with COPD had similar patterns of reductions; the DD estimate was approximately -0.13 in post years and statistically significant. We also observed signs of reductions in ED visits and hospitalizations for those with heart disease, but they were not statistically significant.
Conclusions: Our study results add to empirical evidence that air pollution control actions benefit people with chronic conditions through pollution exposure reductions and health outcome improvements. Our investigation also contributes to scientific knowledge regarding how to assess the health effects of longer-term, large scale, and complex regulatory actions with routinely collected medical claims data.