Variables were included in the model if they were biologically plausible and associated with the outcome of interest in univariate analysis (P < 0.1 or odds ratio ≥ 2.0 for nominal variables, or a median split of continuous variables).
For this purpose, the sample was divided by median split on the respective variable (e.g., age) and pair wise comparisons using t-tests and effect sizes d were conducted.
Each log-linear variable was obtained by applying a median split to its corresponding continuous variable.
Finally, when we stratified women by parity and OC use, we observed no difference in average levels of salivary 17β-estradiol between the four groups of women defined by median split of the two variables (P = 0.19, age-adjusted).
Although we observed similar patterns of results using the dichotomized predictive variables (median split), none of the comparisons were statistically significant except for baseline ACTH, which was higher in the higher BPb group (p = 0.032); mean [95% confidence intervals (CIs)] were 18.4 pg/mL (15.4 21.8) for the low BPb group and 21.5 pg/mL (17.9 25.7) for the high BPb group.
In the logistic regression models, alcohol consumption during the past year was used as a categorical variable, and the median split of mammographic density phenotypes was used as the dependent variable.
Cox & Snell R2 0.12, Nagelkerke R2 0.19 MHTP = Mental health problems in need of treatment, KI = Karolinska Institutet SSE = Stockholm School of Econonomics † variable dichotomised by median split, scale range for all 1-4.
For our linear mixed effects model, methylation levels, despite the potential loss of statistical power, were treated as a binary variable after a median split.
To examine whether participants' educational background a rough indicator of their subscription to the scientific worldview moderated effects, we first converted education to a dichotomous variable based on a median split (college graduates vs. "some college" or less).
All variables were dichotomized using median split.
