title: Are two really better than one? Empirical examination of repeat blood pressure measurements and stroke risk in the Renfrew/Paisley and collaborative studies.
abstract: OBJECTIVE
  Blood pressure measured on 2 occasions in 2 large prospective cohort studies in Scotland was related to stroke, defined as stroke mortality or hospital admission for stroke. The purpose was to investigate whether 2 blood pressure readings gave a more accurate estimate of stroke risk over a long follow-up period than 1 reading.
  
  
  METHODS
  In the 1970s, the Renfrew/Paisley general population study investigated 3060 men and 3502 women and the Collaborative study investigated 2683 employed men on 2 occasions. The mean years between screening were 4 and 5, respectively. Blood pressure measured on the 2 occasions was related to stroke risk in 17-year and 21-year follow-up periods after the second screening, respectively.
  
  
  RESULTS
  For both systolic and diastolic blood pressure, the mean of the measures on the 2 occasions, the maximum of the 2 measures and the measure corrected for regression dilution was more strongly related to stroke over the follow-up periods than either single measure.
  
  
  CONCLUSIONS
  Two blood pressure measurements seem better than 1 for indicating stroke risk. Underestimation using single measures will lead to both misclassification of the risk of disease for individuals and also the population-attributable risk of disease associated with elevated blood pressure.
authors.affiliation: West of Scotland Cancer Surveillance Unit, Department of Public Health, University of Glasgow, Glasgow, UK. c.l.hart@udcf.gla.ac.uk
authors.forename: C L
authors.initials: CL
authors.lastname: Hart
authors.forename: D J
authors.initials: DJ
authors.lastname: Hole
authors.forename: G
authors.initials: G
authors.lastname: Davey Smith
mesh_terms: D000328:Adult; D001795:Blood Pressure Determination; D036262:Empirical Research; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D012307:Risk Factors; D020521:Stroke / Q000453:epidemiology*