Reply: —We appreciate Dr. Nardone's comments and his interest in our paper. We concur with Dr. Nardone that spirometry must be done in people with prolonged forced expiratory time.

As we stated in our article, forced expiratory time is not sufficient on its own to diagnose chronic obstructive pulmonary disease.1 Likelihood ratios greater than 10 and less than 0.10 are very useful in either ruling in or ruling out a target disorder.2 The pretest probability of disease becomes particularly important when likelihood ratios are between 0.10 and 10. In our previous paper, we stated that if the patient's pretest probability is 10%,3 and applying a likelihood ratio of 0.3, the posttest probability is sufficiently low that we would feel comfortable in ruling out the disease. However, if the pretest probability for a particular patient were higher, the posttest probability would be higher, such that we might not be comfortable ruling out the disease. Finally, the combined likelihood ratio of 59 was obtained from multiplying the adjusted likelihood ratios (adjusted for their nonindependence), not from the crude likelihood ratios. Therefore, they cannot be used directly to calculate sensitivity and specificity.—Sharon E. Straus, MD, Finlay A. Mc Alisters, On Behalf of the CARE-COAD Investigators.Toronto General Hospital, Toronto, Ontario, Canada.


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  • 1
    Straus SE , McAlister FA , Sackett DL , Deeks JJ , On Behalf of the CARE-COAD2 Investigators. Accuracy of history, wheezing, and forced expiratory time in the diagnosis of chronic obstructive pulmonary disease. J Gen Intern Med. 2002;17: 6848.
  • 2
    Badgett RG , Tanaka DJ , Hunt DK , et al. Can moderate chronic obstructive pulmonary disease be diagnosed by historical and physical findings alone? Am J Med. 1993;94: 18896.
  • 3
    Sackett DL , Straus SE , Richardson WS , Rosenberg WM , Haynes RB . Evidence-based Medicine: How to Practise and Teach It. London: Harcourt Brace; 2000.