Why was no control group studied?

EDITOR —Thiadens et al examined 192 patients presenting to their general practitioner with persistent cough —a common and challenging problem in primary care —and found a high prevalence of asthma (39%) and chronic obstructive pulmonary disease (7%).1 I was disappointed that they did not provide a control group of asymptomatic subjects in the community.

What is the prevalence of abnormal results of pulmonary function tests in their general population? If it is high, with a prevalence approaching the prevalence found in their population of patients with cough, an alternative conclusion might be that asthma and chronic obstructive pulmonary disease are common and not significantly more common in the population of patients with cough. I encourage Thiadens et al to examine their study group further. One issue deserving scrutiny is whether these patients are still coughing after six months. Also, what diagnoses (if any) apply to the remaining (54%) patients with cough, and does their prognosis differ from that of the group diagnosed as having asthma and chronic obstructive pulmonary disease? Finally, how do these patients respond to different treatments?

Children with cough alone should not be labelled asthmatic

EDITOR —Thiadens et al devised a score to estimate the probability of asthma or chronic obstructive pulmonary disease in patients who present …