Smoker, ex-smoker or non-smoker? The validity of routinely recorded smoking status in UK primary care: a cross-sectional study

BMJ Open. 2014 Apr 23;4(4):e004958. doi: 10.1136/bmjopen-2014-004958.


Objective: To investigate how smoking status is recorded in UK primary care; to evaluate whether appropriate multiple imputation (MI) of smoking status yields results consistent with health surveys.

Setting: UK primary care and a population survey conducted in the community.

Participants: We identified 354 204 patients aged 16 or over in The Health Improvement Network (THIN) primary care database registered with their general practice 2008-2009 and 15 102 individuals aged 16 or over in the Health Survey for England (HSE).

Outcome measures: Age-standardised and age-specific proportions of smokers, ex-smokers and non-smokers in THIN and the HSE before and after MI. Using information on time since quitting in the HSE, we estimated when ex-smokers are typically recorded as non-smokers in primary care records.

Results: In THIN, smoking status was recorded for 84% of patients within 1 year of registration. Of these, 28% were smokers (21% in the HSE). After MI of missing smoking data, the proportion of smokers was 25% (missing at random) and 20% (missing not at random). With increasing age, more were identified as ex-smokers in the HSE than THIN. It appears that those who quit before age 30 were less likely to be recorded as an ex-smoker in primary care than people who quit later.

Conclusions: Smoking status was relatively well recorded in primary care. Misclassification of ex-smokers as non-smokers is likely to occur in those quitting smoking at an early age and/or a long time ago. Those with no smoking status information are more likely to be ex-smokers or non-smokers than smokers.


Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Age Factors
  • Aged
  • Aged, 80 and over
  • Cross-Sectional Studies
  • Electronic Health Records*
  • England / epidemiology
  • Female
  • Health Surveys*
  • Humans
  • Male
  • Middle Aged
  • Primary Health Care / statistics & numerical data*
  • Smoking / epidemiology*
  • Smoking Cessation / statistics & numerical data*
  • Young Adult