Smoking prevalence in the European Union: a comparison of national and transnational prevalence survey methods and results.

Objectives: To determine whether the European Commission Eurobarometer survey of 27 European Union (EU) member states produces reliable smoking prevalence estimates when compared to national prevalence survey data, and to identify approaches to standardising the measurement of smoking prevalence in the EU.
Methods: This was a direct comparison of questions, sampling methods and smoking prevalence estimates, between the 2006 Eurobarometer study and contemporaneous national surveys. All 27 EU member states were included. Participants were people surveyed in the 2006 Eurobarometer study and in various national surveys in the closest year to 2006 for which data were available. The main outcome measures were the mean and range of differences in prevalence estimates between the Eurobarometer and national surveys.
Results: Most national surveys used similar multistage sampling methods and involved sample sizes of 3000 or more, but the phrasing of the questions used to define smoking, the inclusion or exclusion of occasional smokers, the age ranges of participants and the frequency of national surveys varied substantially between countries. The Eurobarometer study used the same questions in all countries but in sample sizes of 1000, or in 3 countries, 500. Eurobarometer 2006 smoking prevalence estimates were on average 0.37 percentage points higher than those in national surveys, but with a 95% range from -10.49 to +11.23 percentage points. At the extremes, the equivalent national prevalence estimate for Slovakia was 13.0% higher and for the UK 10.0% lower than the Eurobarometer figure.
Conclusions: Measurements of the prevalence of smoking, the biggest avoidable public health threat in the European Union, are highly discrepant within countries between national and European Commission survey estimates. Monitoring national smoking prevalence on a regular basis, using standardised methods in representative population samples, is an urgent priority for the EU.