title: Influence of exposure differences on city-to-city heterogeneity in PM2.5-mortality associations in US cities.
abstract: Multi-city population-based epidemiological studies have observed heterogeneity between city-specific fine particulate matter (PM2.5)-mortality effect estimates. These studies typically use ambient monitoring data as a surrogate for exposure leading to potential exposure misclassification. The level of exposure misclassification can differ by city affecting the observed health effect estimate.
  
  
  
  The objective of this analysis is to evaluate whether previously developed residential infiltration-based city clusters can explain city-to-city heterogeneity in PM2.5mortality risk estimates. In a prior paper 94 cities were clustered based on residential infiltration factors (e.g. home age/size, prevalence of air conditioning (AC)), resulting in 5 clusters. For this analysis, the association between PM2.5and all-cause mortality was first determined in 77 cities across the United States for 2001-2005. Next, a second stage analysis was conducted evaluating the influence of cluster assignment on heterogeneity in the risk estimates.
  
  
  
  Associations between a 2-day (lag 0-1 days) moving average of PM2.5concentrations and non-accidental mortality were determined for each city. Estimated effects ranged from -3.2 to 5.1% with a pooled estimate of 0.33% (95% CI: 0.13, 0.53) increase in mortality per 10 μg/m3increase in PM2.5. The second stage analysis determined that cluster assignment was marginally significant in explaining the city-to-city heterogeneity. The health effects estimates in cities with older, smaller homes with less AC (Cluster 1) and cities with newer, smaller homes with a large prevalence of AC (Cluster 3) were significantly lower than the cluster consisting of cities with older, larger homes with a small percentage of AC.
  
  
  
  This is the first study that attempted to examine whether multiple exposure factors could explain the heterogeneity in PM2.5-mortality associations. The results of this study were found to explain a small portion (6%) of this heterogeneity.
authors.affiliation: National Health and Environmental Effects Research Laboratory, United States Environmental Protection Agency, 109 T.W. Alexander Drive, Research Triangle Park, NC, 27711, USA. Baxter.lisa@epa.gov.
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Baxter
authors.affiliation: National Health and Environmental Effects Research Laboratory, United States Environmental Protection Agency, 109 T.W. Alexander Drive, Research Triangle Park, NC, 27711, USA.|Present address: Division of Biostatistics and Bioinformatics and Department of Biomedical Research, National Jewish Health, 1400 Jackson St., Denver, CO, 80206, USA.|Department of Epidemiology, Colorado School of Public Health, 13001 E. 7th Place, Aurora, CO, 80045, USA.
authors.forename: James L
authors.initials: JL
authors.lastname: Crooks
authors.affiliation: National Center for Environmental Assessment, United States Environmental Protection Agency, 109 T.W. Alexander Drive, Research Triangle Park, NC, 27711, USA.
authors.forename: Jason D
authors.initials: JD
authors.lastname: Sacks
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000393:Air Pollutants / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D002947:Cities / Q000453:epidemiology; D016000:Cluster Analysis; D004781:Environmental Exposure / Q000009:adverse effects / Q000032:analysis*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008875:Middle Aged; D009026:Mortality; D052638:Particulate Matter / Q000032:analysis*; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter
keywords: Cluster analysis; Epidemiology; Exposure; Meta-regression; Particulate matter