Data and statistical analysis
The data and statistical analyses complied with the recommendations of experimental design and analysis in pharmacology (Curtis et al., 2018). The data were analyzed using GraphPad Prism version 7.1a. A p-value of <0.05 was considered statistically significant.
GEO multiarray statistical analysis
Nonparametric unpaired Mann-Whitney U-tests were used to test differences in CYP2A13, CYP2A6 and CYP2A7 expression levels between smokers and non-smokers in the small airway epithelium of the lung in GEO datasets: GSE30063 and GSE108134.
For GSE11874, the D’Agostino-Pearson omnibus normality test was used to determine the normality of signal distribution of CYP2A13, CYP2A6 and CYP2A7 expression levels in smokers’ small airway epithelium of the lung, followed by correlation analyses to assess the relationship between CYP2A13, CYP2A6 and CYP2A7 expression levels and pack-year data, within smokers.