I am currently fitting a linear mixed-effects model to my data where the outcome variable can have both positive and negative values (integers).
The issue now is, that my outcome data is skewed with a heavier tail in the positive direction. As a consequence, my residuals (as plotted with a qqnorm plot) deviate from a qq line in both directions.
Usually, I would go ahead and do something like a log-transformation, but in this case this is not possible as I have both positive and negative data. Using a generalized linear mixed-effects model does not solve my problem as well due to similar reasons (negative data).
A further thing to note is that I have a lot of data (multiple millions of samples).