Effective Skill Level

The effective skill level is the level at which a particular skill is considered to be when using the skill. It is a combination of the base skill level, any abilities, spells, etc. that affect that skill, and base luck. At default, effective skill level is

Base Skill Level + Benefits (Spells, ModAV, etc.) - 
                   Determents (negative Spells, ModAV, etc.) + .4(Luck - 50)

Note that if your luck falls below 50 it will count as a penalty towards all of your skills.