Authors' reply

BMJ 1996; 312 doi: https://doi.org/10.1136/bmj.312.7046.1607c (Published 22 June 1996) Cite this as: BMJ 1996;312:1607
  1. Roger Buchdahl,
  2. Tabitha Stebbings,
  3. Abdel Babiker,
  4. Alison Parker
  1. Consultant paediatrician Hillingdon Hospital, Middlesex UB8 3NN
  2. Senior environmental health officer London Borough of Hillingdon, Environmental Protection Unit, Uxbridge UB8 1UN
  3. Senior lecturer in epidemiology MRC HIV Clinical Trials Centre, University College of London Medical School, London WC1E 6AU
  4. Paediatric respiratory nurse Hillingdon Hospital, Middlesex UB8 3NN

    EDITOR,—The implied criticism by Merion R Evans and colleagues of not using an a priori hypothesis in our study perhaps fails to appreciate that the study was observational, undertaken in response to the controversy concerning air pollution and childhood asthma. The findings have not emerged as a result of performing “a series of complex statistical tests,” as can be seen from the plots of the raw data.

    The following a posteriori hypotheses may be made. Firstly, there may by a critical concentration of ozone which has a …

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