Principal component and multivariate vector length analysis of upper vs lower lobe gene expression of known smoking-responsive genes [25].

A. Principal component analysis (PCA) of the 529 probe sets of the smoking responsive list. Red = upper lobe samples; blue = lower lobe samples. The line connecting the red and blue data points connects the upper and lower lobe samples from the same individual. B. Plot of the distribution of the median distance between the upper and lower lobe samples for each individual in the space of 529 probe sets in the smoking- responsive list as measured by vector length (red circle) compared to the distribution of median distances between upper and lower lobe samples for 100 sets of 529 probe sets selected at random from the genome-wide list of probe sets present in at least 20% of the samples, minus the 529 smoking-responsive list (boxplot: middle bar is overall median, box contains the inner quartiles, and the whiskers, the 0.95 quartiles).