Generating pre-test probabilities: a neglected area in clinical decision making

John R Attia, David W Sibbritt, Ben D Ewald, Balakrishnan R Nair, Neil S Paget, Rod F Wellard, Lesley Patterson and Richard F Heller
Med J Aust 2004; 180 (9): 449-454.


Objective: To assess the accuracy and variability of clinicians’ estimates of pre-test probability for three common clinical scenarios.

Design: Postal questionnaire survey conducted between April and October 2001 eliciting pre-test probability estimates from scenarios for risk of ischaemic heart disease (IHD), deep vein thrombosis (DVT), and stroke.

Participants and setting: Physicians and general practitioners randomly drawn from College membership lists for New South Wales and north-west England.

Main outcome measures: Agreement with the “correct” estimate (being within 10, 20, 30, or > 30 percentage points of the “correct” estimate derived from validated clinical-decision rules); variability in estimates (median and interquartile ranges of estimates); and association of demographic, practice, or educational factors with accuracy (using linear regression analysis).

Results: 819 doctors participated: 310 GPs and 288 physicians in Australia, and 106 GPs and 115 physicians in the UK. Accuracy varied from about 55% of respondents being within 20% of the “correct” risk estimate for the IHD and stroke scenarios to 6.7% for the DVT scenario. Although median estimates varied between the UK and Australian participants, both were similar in accuracy and showed a similarly wide spread of estimates. No demographic, practice, or educational variables substantially predicted accuracy.

Conclusions: Experienced clinicians, in response to the same clinical scenarios, gave a wide range of estimates for pre-test probability. The development and dissemination of clinical decision rules is needed to support decision making by practising clinicians.

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  • John R Attia1
  • David W Sibbritt2
  • Ben D Ewald3
  • Balakrishnan R Nair4
  • Neil S Paget5
  • Rod F Wellard6
  • Lesley Patterson7
  • Richard F Heller8

  • 1 Centre for Clinical Epidemiology and Biostatistics, University of Newcastle, Newcastle, NSW.
  • 2 Department of Medicine, John Hunter Hospital, New Lambton, NSW.
  • 3 The Royal Australasian College of Physicians, Sydney, NSW.
  • 4 Royal Australian College of General Practitioners, South Melbourne, VIC.
  • 5 Evidence for Population Health Unit, University of Manchester, Manchester, UK.


Competing interests:

None identified.

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