Psychological confounds in medical research: the example of excessive cough in asthma

This experiment tested the hypothesis that the setting in which research is conducted may dominate symptom magnitude. Cough was induced with inhaled c itric acid and its magnitude was influenced by changing the setting in 30 a dolescents with asthma, Cough thresholds for citric acid were determined. T he participants were assigned to a condition emphasising asthma, or a contr ol condition, described as estimation of lemon flavors. All participants in haled (in different order) thresholds for citric acid, 50% of these thresho lds, or placebo, Results showed that both cough frequency and subjective 'cough tendency' we re significantly higher in the asthma condition. State anxiety was higher i n the asthma condition, but correlated only moderately with cough. Lung fun ction, severity of asthma, trait anxiety, age or sex did not correlate with cough. It was concluded that patients with asthma cough more often in a situation which they have learned to associate with asthma. (C) 2000 Elsevier Science Ltd. All rights reserved.