Approaches for identifying persons with asthma

Method	Problems
Clinical evaluation	Nonstandardization of physician criteria for diagnosis; bias toward more severe cases; bias by access to physician
Questionnaire history of diagnosis	Same as above; plus recall bias in subjects
Questionnaire history of symptoms	Possibly influenced by frequency of other symptoms; less specific than physician's diagnosis
Response to bronchodilator	May be influenced by level of FEV₁*; may lack sensitivity
Bronchoconstrictor response	Influenced by level of FEV₁*; may be nonspecific

FEV₁: forced expiratory volume in one second.
* Based on Poiseuille's Law; the resistance of the airway is inversely proportional to the radius raised to the 4^th power (r4). Thus, airways that are of smaller caliber only need a small change in radius to significantly change the resistance, and hence, FEV₁.

Adapted from: Weiss ST, Speizer FE. Epidemiology and natural history. In: Bronchial Asthma: Mechanisms and Therapeutics, 3rd ed, Weiss EB, Stein M (Eds), Little, Brown, Boston 1993.

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Approaches for identifying persons with asthma