Can data from primary care medical records be used to monitor national smoking prevalence?

BACKGROUND: Data from primary care records could potentially provide more comprehensive population-level information on smoking prevalence at lower cost and in a more timely fashion than commissioned national surveys. Therefore, we compared smoking prevalence calculated from a database of primary care electronic medical records with that from a 'gold standard' national survey to determine whether or not medical records can provide accurate population-level data on smoking.
METHODS: For each year from 2000 to 2008, the annual recorded prevalence of current smoking among patients in The Health Improvement Network (THIN) Database was compared with the 'General Household Survey (GHS)-predicted prevalence' of smoking in the THIN population, calculated through indirect standardisation by applying age-, sex- and region-specific smoking rates from the corresponding GHS to the THIN population.
RESULTS: Completeness of smoking data recording in THIN improved steadily in the study period. By 2008, there was good agreement between recorded smoking prevalence in THIN and the GHS-predicted prevalence; the GHS-predicted prevalence of current smoking in the THIN population was 21.8% for men and 20.2% for women, and the recorded prevalence was 22.4% and 18.9%, respectively.
CONCLUSIONS: The prevalence of current smoking recorded within THIN has converged towards that which would be expected if GHS smoking rates are applied to the THIN population. Data from electronic primary care databases such as THIN may provide an alternative means of monitoring national smoking prevalence.