I performed zlmfit on a matrix with MAST for 2 populations of cells, A and B, with population A as intercept. Then I run gseaAfterBoot on the zlfit object after performing bootstrapping with bootVcov1. If I get a positive value Z score for a particular gene set, does it mean that genes in this geneset are upregulated in population A compared to B? Similarly, a negative Z score mean that genes in this geneset are downregulated in A compared to B. Or is it the other way round? Not sure of the directionality here, because I am not sure what the model coefficients that were used to calculate the Z score mean.