title: Meta-analysis of the association between secondhand smoke exposure and physician-diagnosed childhood asthma.
abstract: BACKGROUND
  Studies suggest an association between secondhand smoke exposure and the development of childhood asthma. Several countries are considering legislation to protect children from exposure.
  
  
  METHODS
  A systematic review was conducted using MEDLINE, Embase, PubMed, and Web of Knowledge databases and a random effects meta-analysis was undertaken. Heterogeneity was assessed using the I (2) test. Publication and small study biases were examined visually using a funnel plot and tested formally using Egger test. Univariate and multivariate meta-regression analyses were undertaken, including a subgroup analysis of cohort studies to examine the effect of duration of follow-up.
  
  
  RESULTS
  Twenty relevant studies were identified (14 cross-sectional, 4 cohort, and 2 case-control) and provided 31 estimates of effect size. The pooled odds ratio was 1.32 (95% CI: 1.23, 1.42, p < .001). There was moderate heterogeneity (I (2) = 74.2%, p < .001). On multivariate meta-regression analysis, effect size estimates were significantly higher for case-control studies (p = .042) and those using self-reported exposure to secondhand smoke (p = .050). There was no evidence of significant publication or small study bias (Egger test, p = .121).
  
  
  CONCLUSIONS
  There is now consistent evidence of a modest association between secondhand smoke and physician-diagnosed childhood asthma. These results lend support to continued efforts to reduce childhood exposure to secondhand smoke.
authors.affiliation: Institute of Health and Wellbeing, University of Glasgow, UK.
authors.forename: Olaitan
authors.initials: O
authors.lastname: Tinuoye
authors.forename: Jill P
authors.initials: JP
authors.lastname: Pell
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Mackay
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000139:chemically induced / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D016017:Odds Ratio; D014028:Tobacco Smoke Pollution / Q000009:adverse effects*
chemical_list: D014028:Tobacco Smoke Pollution