title: Linkage of survey data with district-level lung cancer registrations: a method of bias reduction in ecological studies.
abstract: OBJECTIVE
  To investigate a stratified ecological method for reducing ecological bias in studies that use aggregate data, by incorporating information on individual-level risk factors into the analysis.
  
  
  METHODS
  Cross-sectional study investigating associations between socioeconomic risk factors and lung cancer in the north of England, using 1991 UK Census Small Area Statistics and Sample of Anonymised Records with lung cancer registrations from three regional cancer registries for 1993-6.
  
  
  METHODS
  92 local authority districts in the north of England containing over three million people aged 45-74 years.
  
  
  RESULTS
  Generally, groups considered more socioeconomically disadvantaged had an increased risk of lung cancer across districts. In the standard ecological analysis, effects for non-car ownership, social class III manual, social class IV/V and socioeconomic inactivity were insignificant, suggesting ecological bias. In the stratified ecological analysis these effects became significant (rate ratio (RR) 2.23, 95% confidence interval (CI) 1.79 to 2.78, p<0.001; RR 1.35, 95% CI 1.04 to 1.74, p = 0.022; RR 2.36, 95% CI 1.86 to 2.99, p<0.001; and RR 0.72, 95% CI 0.53 to 0.98, p = 0.039, respectively), and spuriously large positive effects for the social class III non-manual (RR 20.29) and unemployment groups (RR 147.53) reduced to a more reasonable level (RR 1.92, 95% CI 1.46 to 2.52, p<0.001; and RR 2.36, 95% CI 1.22 to 4.55, p = 0.011, respectively).
  
  
  CONCLUSIONS
  Stratified ecological analysis incorporating information on individual-level covariates reduced the bias seen in a standard ecological analysis. The method is straightforward to apply and allows the linkage of health data with data from any large-scale complex survey where district of residence is known.
authors.affiliation: Centre for Medical Statistics and Health Evaluation, University of Liverpool, Liverpool, L69 3GS, UK. g.lancaster@liv.ac.uk
authors.forename: Gillian A
authors.initials: GA
authors.lastname: Lancaster
authors.forename: Mick
authors.initials: M
authors.lastname: Green
authors.forename: Steven
authors.initials: S
authors.lastname: Lane
mesh_terms: D000328:Adult; D000368:Aged; D015982:Bias; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012042:Registries; D012307:Risk Factors; D012959:Socioeconomic Factors