title: Biased risk factor assessment in prospective studies of peripheral arterial disease due to change in exposure and selective mortality of high-risk individuals.
abstract: BACKGROUND
  Our aim was to assess whether risk factor assessment in prospective studies of peripheral disease (PAD) might be biased by change in exposure and selective mortality of individuals at high risk.
  
  
  METHODS
  The cohort 'Men born in 1914' has been followed since the baseline examination 1969. PAD, (i.e. ankle-brachial pressure index < 0.9) at the age of 68 was related to risk factors measured at the age of 55 and 68.
  
  
  RESULTS
  Hypertension was present in 64% of the men. Of these, 62% were normotensive at 55. Men with hypertension at the age of 55 had lower odds for PAD (odds ratio 1.9; 95% CI 0.8-4.5) than men who were normotensive at 55 (odds ratio 3.0. 95% CI 1.5-6.1). One-third remained smokers at 68; 27% were ex-smokers. The odds for PAD was 3.0 times higher (95% CI 1.4-6.3) in ex-smokers and 2.6 times higher (95% CI 1.3-5.4) in current smokers than in non-smokers. Less than half remained in the same cholesterol quartile. The odds for PAD was 1.5 (95% CI 0.8-2.8) in men with hypercholesterolaemia at 68 and 2.2 (95% CI 1.1-4.7) in men with hypercholesterolemia at both examinations. Smoking and hypertension at the age of 55 were both associated with an increased mortality rate: 26% Of the smokers and 31% of the men with hypertension died before the age of 68.
  
  
  CONCLUSIONS
  Risk factor assessment in prospective studies of PAD is affected by change in exposure and selective mortality of individuals at high risk.
authors.affiliation: Department of Community Medicine, Lund University, Malmö University Hospital, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Ogren
authors.forename: B
authors.initials: B
authors.lastname: Hedblad
authors.forename: L
authors.initials: L
authors.lastname: Janzon
mesh_terms: D000368:Aged; D001158:Arteries; D015982:Bias; D006801:Humans; D006937:Hypercholesterolemia / Q000150:complications; D006973:Hypertension / Q000150:complications; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D016491:Peripheral Vascular Diseases / Q000453:epidemiology* / Q000209:etiology / Q000401:mortality; D011446:Prospective Studies; D012044:Regression Analysis; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects; D013548:Sweden / Q000453:epidemiology