Year: 2013
Type: letter
Abstract: Number needed to treat in COPD: exacerbations versus pneumonias 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 treat-ment 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 exacer-bations that account for multiple events.3 The paper states that ‘the proper calcu-lation resulted in a NNT of 14 patients who need to be treated for 1 year to prevent one COPD exacerbation’. This interpretation of the patient-based NNT is incorrect. As the only data used is the time of the first exacerbation, the calcula-tion performed is of the NNT needed to prevent one patient from experiencing any exacerbations in the year. For the Towards a Revolution in COPD Health (TORCH) study, the author con-verts event rates to probabilities of an event using a formula based on the Poisson distribution, which does not account for the correlation of events within an individ-ual. This calculation gives incorrect estimates of incidence rates and, therefore, the patient-based NNT for TORCH is considerably wrong. This error is surpris-ing as Dr Suissa has criticised others for neglecting this extra-Poisson variability.3
Source: Thorax
Language: English
Subfield: Pulmonary and Respiratory Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2104291620