title: Number needed to treat: analyzing of the effectiveness of thoracoabdominal aortic repair.
abstract: BACKGROUND
  Number needed to treat (NNT) is a method used to calculate the number of patients who need to be treated to prevent one adverse outcome. To analyze the effectiveness of thoracoabdominal and descending thoracic aortic aneurysm repair, we computed the NNT required to prevent one death.
  
  
  METHODS
  Between Jan 1991 and Feb 2003, we repaired 1004 aneurysms of the descending thoracic and thoracoabdominal aorta. We followed the patients from surgery until death. Five-year actuarial survival in our population was computed by the Kaplan-Meier method. Natural history data for comparison were taken from the population-based work of Bickerstaff et al., 1982. NNT was calculated as the reciprocal of the risk difference at 5 years. 95% confidence intervals were computed by the method of Daly.
  
  
  RESULTS
  Five-year mortality in the population-based cohort was 87 vs. 39% in our treated population, for a risk difference of 48%. 1/0.48=2, indicating that two patients need to be treated to prevent one death at 5 years (95% CI 1.8-2.5, p<0.0001).
  
  
  CONCLUSIONS
  An NNT of two demonstrates the effectiveness of surgical repair of descending thoracic and thoracoabdominal aortic aneurysms when compared to the natural history. By comparison, carotid endarterectomy for symptomatic lesions >70% has an NNT of 15 to prevent a single stroke or death. NNT can also be applied to aneurysm size criteria to estimate the effort required to prevent death or rupture for a given aneurysm size.
authors.affiliation: The Department of Cardiothoracic and Vascular Surgery, University of Texas Health Science Center at Houston, Medical School, Houston, TX 77030, USA.
authors.forename: C C
authors.initials: CC
authors.lastname: Miller
authors.forename: E E
authors.initials: EE
authors.lastname: Porat
authors.forename: A L
authors.initials: AL
authors.lastname: Estrera
authors.forename: A N
authors.initials: AN
authors.lastname: Vinnerkvist
authors.forename: T T T
authors.initials: TT
authors.lastname: Huynh
authors.forename: H J
authors.initials: HJ
authors.lastname: Safi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017544:Aortic Aneurysm, Abdominal / Q000401:mortality* / Q000601:surgery*; D017545:Aortic Aneurysm, Thoracic / Q000401:mortality* / Q000601:surgery*; D002648:Child; D015331:Cohort Studies; D005260:Female; D006301:Health Services Needs and Demand / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D016019:Survival Analysis; D016896:Treatment Outcome