All statistical tests were performed using GraphPad Prism, GraphPad StatMate 2.0, and the R statistical software package. Regression analysis was used to test for correlations between rs1800693 genotype and TNFR1 transcript levels and TNFR1 cell surface expression in human immune cell subsets, assuming a linear genotype-to-phenotype relationship (1 d.f. F-test); age and sex were not included as covariates as for all data sets no age or sex effects were observed (P>0.05). For the TNFR1_Δ6 transcripts the slope calculated by the linear regression analysis for the CD14+ monocytes, polymorphonuclear cells and CD3+ T cells was 0.0014, 0.0026 and 0.0003, respectively. Using a Bonferroni correction for multiple testing (taking P = 0.05 and considering three independent hypotheses for the three different human immune cell subsets for RNA-level analyses), the significance threshold estimated was P = 0.017. At this significance threshold we obtained >90% power to detect the differences observed with our sample size. The percentage of TNFR1_Δ6 transcript level variation accounted for by genotype at rs1800693 was estimated by least-squares regression analysis at 67, 52 and 55% for the CD14+ monocytes, polymorphonuclear
