Letter

Incidence of hospital admission does not equal incidence of disease

BMJ 2000; 320 doi: 10.1136/bmj.320.7244.1277 (Published 6 May 2000)
Cite this as: BMJ 2000;320:1277.1

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Conclusions drawn from data are incorrect

  1. Louis H Pobereskin, consultant neurosurgeon (louis.pobereskin@phnt.swest.nhs.uk),
  2. J Robert Sneyd, consultant anaesthetist
  1. Derriford Hospital, Plymouth PL6 8DH
  2. Epidemiology, Institute of Public Health, Odense University, University of Southern Denmark, DK 5000 Odense C, Denmark
  3. Department of Biostatistics, University of Aarhus, DK 8000 Aarhus, Denmark
  4. Department of Neurology, Odense University Hospital, Odense, Denmark
  5. Danish Epidemiology Science Centre, University of Aarhus, DK 8000 Aarhus, Denmark
  6. Department of Clinical Epidemiology of Aarhus and Aalborg University Hospitals at the Institute of Epidemiology and Social Medicine, University of Aarhus, DK 8000 Aarhus, Denmark

    EDITOR—We are concerned about Gaist and colleagues' methods and feel that the conclusions they draw from their data are incorrect.1

    The diagnosis of subarachnoid haemorrhage was validated in a sample from only one county. Is Funen County representative of Denmark, and how was it selected? Hospitals with 10 or fewer registered patients in the study period were excluded. Why was it appropriate to exclude the smaller hospitals when they may be a source of patients with particularly low predictive value for a registered diagnosis of subarachnoid haemorrhage?

    The cohort of first degree relatives was overwhelmingly made up of children, and theywere the only group in table 2 for whom the incidence rate ratios were significantly different from 1 The main problem with the study is one that plagues much of the literatureon subarachnoid haemorrhage—it was hospital based. The strongest predictor of survival in subarachnoid haemorrhage is age. This is just …

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