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Correspondence
Number needed to treat in COPD: exacerbations versus pneumonias
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  1. Oliver N Keene1,
  2. Antonio Anzueto2,
  3. Gary T Ferguson3,
  4. Peter M A Calverley4
  1. 1Clinical Statistics, GlaxoSmithKline, Uxbridge, UK
  2. 2Pulmonary/Critical Care Division, University of Texas Health Science Center, San Antonio, Texas, USA
  3. 3Pulmonary Research Institute of Southeast Michigan, Livonia, Michigan, USA
  4. 4School of Aging and Chronic Disease, University of Liverpool, Liverpool, UK
  1. Correspondence to Oliver N Keene, Clinical Statistics, GlaxoSmithKline, 1-3 Iron Bridge Road, Uxbridge UB11 1BT, UK; oliver.n.keene{at}gsk.com

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Number needed to treat (NNT) is an attractive concept for clinicians, but its application to a treatment that reduces the frequency of COPD exacerbations is not straightforward. Dr Suissa1 proposes a method for calculating the NNT based on the Kaplan–Meier curve of time to first exacerbation. This approach ignores all exacerbations beyond the first one experienced by the patient and does not appropriately reflect the benefit of a treatment that reduces multiple exacerbations in the same patient.2 From a statistical viewpoint, the approach is not efficient as it does not use all the exacerbation data collected. Dr Suissa has himself previously advocated methods of analysis of exacerbations …

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