My character's resistance is listed on the details pane when I open my inventory, and it's a simple integer. It appears to undergo some type of calculation to determine the percentage of damage each of these actually counts for:
Judging by the tooltip, there's some factor based on enemy (and/or my?) level. I believe these numbers are 80 due to my intelligence - I had 798 at the time this was taken.
How is percentage resistance calculated? Although the base "Resistance" integer appears to be derived directly from my stats, does the percentage in this tooltip take into account skills, enchantments, or other modifiers that change resistance?