title: Estimating error in using residential outdoor PM2.5 concentrations as proxies for personal exposures: a meta-analysis.
abstract: BACKGROUND
  Studies examining the health effects of particulate matter <or= 2.5 microm in aerodynamic diameter (PM2.5) commonly use ambient PM2.5 concentrations measured at distal monitoring sites as proxies for personal exposure and assume spatial homogeneity of ambient PM2.5. An alternative proxy-the residential outdoor PM2.5 concentration measured adjacent to participant homes-has few advantages under this assumption.
  
  
  OBJECTIVE
  We systematically reviewed the correlation between residential outdoor PM2.5 and personal PM2.5 (-rj) as a means of comparing the magnitude and sources of measurement error associated with their use as exposure surrogates.
  
  
  METHODS
  We searched seven electronic reference databases for studies of the within-participant residential outdoor-personal PM2.5 correlation.
  
  
  RESULTS
  The search identified 567 candidate studies, nine of which were abstracted in duplicate, that were published between 1996 and 2008. They represented 329 nonsmoking participants 6-93 years of age in eight U.S. cities, among whom -rj was estimated (median, 0.53; range, 0.25-0.79) based on a median of seven residential outdoor-personal PM2.5 pairs per participant. We found modest evidence of publication bias (symmetric funnel plot; pBegg = 0.4; pEgger = 0.2); however, we identified evidence of heterogeneity (Cochran's Q-test p = 0.05). Of the 20 characteristics examined, earlier study midpoints, eastern longitudes, older mean age, higher outdoor temperatures, and lower personal-residential outdoor PM2.5 differences were associated with increased within-participant residential outdoor-personal PM2.5 correlations.
  
  
  CONCLUSIONS
  These findings were similar to those from a contemporaneous meta-analysis that examined ambient-personal PM2.5 correlations (rj = median, 0.54; range, 0.09-0.83). Collectively, the meta-analyses suggest that residential outdoor-personal and ambient-personal PM2.5 correlations merit greater consideration when evaluating the potential for bias in studies of PM2.5-mediated health effects.
authors.affiliation: Department of Epidemiology, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina 27514 , USA. christy_avery@unc.edu
authors.forename: Christy L
authors.initials: CL
authors.lastname: Avery
authors.forename: Katherine T
authors.initials: KT
authors.lastname: Mills
authors.forename: Ronald
authors.initials: R
authors.lastname: Williams
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: McGraw
authors.forename: Charles
authors.initials: C
authors.lastname: Poole
authors.forename: Richard L
authors.initials: RL
authors.lastname: Smith
authors.forename: Eric A
authors.initials: EA
authors.lastname: Whitsel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D004782:Environmental Health; D004784:Environmental Monitoring / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D019570:Inhalation Exposure / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D052638:Particulate Matter / Q000008:administration & dosage* / Q000633:toxicity*; D014481:United States; D055815:Young Adult
chemical_list: D052638:Particulate Matter