A complete list of all 172 ILs investigated in this study can be found in the Additional file 1. Fig. 8 Schematic structures representing cations of each IL sub-group tested in this work: a imidazolium, b ammonium, c phosphonium, d pyridinium, e pyrrolidinium, and f sulfonium.
Differences between sub-groups were tested using ANOVA in the case of continuous variables and chi-square in the case of categorical variables.
The differences in the mean values (mean ± standard error) of the cardiometabolic risk factor variables between the sub-groups were tested separately for each of the two groups (normal weight and overweight/obese) by analysis of covariance, adjusting for age, race and sex wherever necessary.
We adjusted for all potential confounders included in the primary analyses except the sub-group factor being tested.
DIF analyses are statistical procedures used to determine to what extent the content of an item affects the item endorsement of sub-groups of test-takers.
DIF analyses, especially when there are several different sub-groups of test-takers, with potentially different characteristics, should not be overlooked.
For DIF in particular, the Rasch model identifies items for which being a member of a certain sub-group of test-takers affects the probability of endorsement of that item when compared to other groups.
Overall, this assessment did in fact seem to hold up reasonably well under DIF scrutiny, so that major concern does not need to be given to differences between sub-groups of test-takers.
Specifically, the authors compared the efficiency of directly testing individual samples to testing sub-groups of samples prior to individual testing.
Sub-group analyses to test for gene-environment interactions were performed by Cox regression with the inclusion of interaction terms between genotype and vitamin D status (25[OH]D < 25 nmol/L vs. ≥ 25 nmol/L); for these analyses, the Benjamini-Hochberg procedure for multiple testing correction was applied to control the false discovery rate with a q value threshold of 0.2 [ 25].
For these sub-tests, post-hoc tests (Tukey B) identified homogeneous sub groups, showing the influence of the socio-demographic factors.
