I have a data set which includes sex, age, and 5 polygenic scores as independent variables, with 16 dependent variables. I have constructed univariate linear mixed effects regression models and corrected for multiple comparisons using the FDR method.
I've also constructed a multivariate model including all the the predictors. Some of the polygenic scores have a significant effect on dependent variable X in the multivariate but not univariate models.
I have a few questions about this:
A) Do I need to correct for multiple comparisons if I have many multivariate linear mixed effects models?
B) It was suggested to me that I use a likelihood ratio test to compare the model with just age and sex to the model with all 5 predictors added at the same time. What unique information would this give me practically?
C) When I ran the likelihood ratio test, I got an insignificant p value for a model which did have a predictor showing a significant effect on the dependent variable. Why this discrepancy?
D) How would I report all of these results? Should I list the effect size and p value from the full models and also the results of the likelihood ratio test?