Fig. 3

Box plot analysis of main discriminant compounds. Box plot of the peak intensities for the 18 statistically downregulated compounds in COPD patients compared to asthmatics. The p-values were calculated by Student t-test and the asterisks show the level of significance between the two groups; * p-values < 0.05, ** p-values < 0.01, *** p-values < 0.001. Box plot analysis was performed by OriginLab^® software