title: A meta-analysis of time-series studies of ozone and mortality with comparison to the national morbidity, mortality, and air pollution study.
abstract: BACKGROUND
  Although many time-series studies of ozone and mortality have identified positive associations, others have yielded null or inconclusive results, making the results of these studies difficult to interpret.
  
  
  METHODS
  We performed a meta-analysis of 144 effect estimates from 39 time-series studies, and estimated pooled effects by lags, age groups, cause-specific mortality, and concentration metrics. We compared results with pooled estimates from the National Morbidity, Mortality, and Air Pollution Study (NMMAPS), a time-series study of 95 large U.S. urban centers from 1987 to 2000.
  
  
  RESULTS
  Both meta-analysis and NMMAPS results provided strong evidence of a short-term association between ozone and mortality, with larger effects for cardiovascular and respiratory mortality, the elderly, and current-day ozone exposure. In both analyses, results were insensitive to adjustment for particulate matter and model specifications. In the meta-analysis, a 10-ppb increase in daily ozone at single-day or 2-day average of lags 0, 1, or 2 days was associated with an 0.87% increase in total mortality (95% posterior interval = 0.55% to 1.18%), whereas the lag 0 NMMAPS estimate is 0.25% (0.12% to 0.39%). Several findings indicate possible publication bias: meta-analysis results were consistently larger than those from NMMAPS; meta-analysis pooled estimates at lags 0 or 1 were larger when only a single lag was reported than when estimates for multiple lags were reported; and heterogeneity of city-specific estimates in the meta-analysis were larger than with NMMAPS.
  
  
  CONCLUSIONS
  This study provides evidence of short-term associations between ozone and mortality as well as evidence of publication bias.
authors.affiliation: Yale University, School of Forestry and Environmental Studies, New Haven, CT 06511, USA. michelle.bell@yale.edu
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Bell
authors.forename: Francesca
authors.initials: F
authors.lastname: Dominici
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Samet
mesh_terms: D000367:Age Factors; D000393:Air Pollutants / Q000633:toxicity*; D000397:Air Pollution / Q000009:adverse effects*; D001499:Bayes Theorem; D002318:Cardiovascular Diseases / Q000401:mortality; D002423:Cause of Death; D006801:Humans; D009026:Mortality; D010126:Ozone / Q000633:toxicity*; D010316:Particle Size; D017594:Publication Bias; D012140:Respiratory Tract Diseases / Q000401:mortality; D013997:Time Factors; D014505:Urban Population / Q000706:statistics & numerical data
chemical_list: D000393:Air Pollutants; D010126:Ozone