The plea for rigorous studies on cough in children.

Although we applaud Khoshoo et al 1 on performing such a comprehensive series of investigations in these 40 children with chronic cough, as reported in a recent issue of CHEST (September 2009), we have major reservations with their conclusions. In particular, we question the assumption that the improvement in cough (assessed at 8 weeks by parent on a subjective visual analog scale cough score) was caused by the respective interventions. In the absence of a control group, this improvement after 8 weeks could simply be due to a period effect 2 and or a placebo effect. 3 , 4 This is particularly likely when the clinicians have taken such a great interest in the child’s cough and have carried out an elaborate series of investigations. This problem is further exacerbated by the manner in which the subjective nature of their outcome measure was measured. Clearly, given the open nature of the intervention, any assessment of outcome must be objective. This time-period effect with cough was well described in the 1980s by Evald and colleagues. 2 Indeed, the placebo effect is reported to be as high as 80% in cough studies. 4