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Incorrect classification: consequences

Naturally, if a test result for airway obstruction is positive, a doctor will be tempted to make the diagnosis and institute treatment or order more tests. If it is negative, the doctor will be more inclined to reject the diagnosis. Each of these decisions comes at a cost and a benefit, in particular if performed with no or only a poor indication (i.e. with low a priori likelihood that the disease is present), such as:

It is not difficult to add more relevant factors. It follows from the above that it is important to strike the optimal balance between true positive and false positive test results. In the case of COPD there is the well-documented benefit of stopping smoking, but little if any benefit from medical treatment except some in the more severe cases [1-2]. Therefore there is every reason to adjust the threshold value for medical intervention (but not for efforts to stop smoking) to a level where we accept fewer false positives and more false negative cases.

References
1 Highland KB, Strange C, Heffner JE. Long-term effects of inhaled corticosteroids on FEV1 in patients with chronic obstructive pulmonary disease: a meta-analysis. Ann Intern Med 2003; 138: 969-973.
2 Burge PS, Lewis SA. So inhaled steroids slow the rate of decline in FEV1 in patients with COPD after all? Thorax 2003; 58: 911-913.
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