Fig. 2
From: Transcriptomic responses in the blood and sputum of cigarette smokers compared to e-cigarette vapers
Principal component analysis reveals outliers and dual users. Principal component analysis (PCA) of RNA-Seq data from all (A) blood samples and (C) sputum samples. (A) A single e-cigarette blood sample was deemed as an outlier (black arrow) and excluded from further blood analysis (note this sample was retained in the sputum group). (C) Two sputum samples from e-cigarette users (black arrows) were observed to cluster with samples from smokers. Analysis of exhaled carbon monoxide in these subjects reveled levels of more than 5 ppm, suggesting that they likely were dual e-cigarette and tobacco users. Samples from these subjects were excluded from further analysis for both blood and sputum. PCA plots for (B) blood and (D) sputum following exclusion of outliers and dual users