Oral N-acetylcysteine (NAC) exerts a beneficial action in chronic bronchitis by reducing the number of exacerbations. Bontognali et al. [1] conducted a randomized, double-blind study to measure the effectiveness of NAC in the long-term treatment of patients with chronic bronchitis and mild airway obstruction. The response is the number of acute exacerbations per month. The mean value and standard deviation for both experimental and placebo group are given below: NAC Placebo Sample size Mean Standard Deviation Sample size Mean Standard Deviation 59 0.11 0.15 70 0.16 0.19