We applied different models such as CpG ~ age + gender + BMI, CpG ~ age + gender + BMI + cell coefficients, and CpG ~ age + gender + BMI + cell coefficients + PCs and monitored the changes in inflation in the genome-wide association studies.
The resulting distribution plots of the white blood cell coefficients for our dataset are presented in Additional file 3: Figure S3.
There were a large number of covariates for each of the association studies, including age, gender, BMI, batch, six white blood cell coefficients, and ten PCs.
For the age association study, the best linear model included the CpG sites and BMI, gender, only two white blood cell coefficients (CD8+T cells and monocytes), and only five PCs (PC4, PC3, PC2, PC10, and PC5) as covariates.
To identify the relevant covariates to include into the final model, we evaluated the effect of including the estimated white blood cell coefficients and the PCs on the p value distribution.
For the smoking association study, the best linear model included the CpG sites and the gender, BMI, age, only two of the cell coefficients (monocytes and granulocytes), only the first PC (PC1), and batch as covariates.
For the gender association study, the best linear model included the CpG sites and age, BMI, only two of the white blood cell coefficients (NK cells and B cells), and only three of the PCs (PC7, PC6, and PC9) as covariates.
Significant differences (P = 0.034) were found in ozone concentration among 1 × 1 km quadrates within the 225 km2 study area, while variability within the 1 × 1 km grid cells (coefficient of variation, CV′ = 0.12) slightly exceed the measurement error (CV′ = 0.08).
Reference cells' coefficient of variation is limited to 5%, automatically.
Pearson correlation analysis demonstrated that the sMICA level was not significantly correlated with the ratio of total NKG2D+ cells (coefficient, 0.034; P = 0.848) or CD3+NKG2D+ cells (coefficient, -0.097; P = 0.585).
In contrast, the sMICA level was negatively correlated with the ratio of CD56+NKG2D+ cells (coefficient, -0.421; P < 0.001).
