Some effects manipulate how random chances are rolled in ways that affect the result without changing the stated chance for the effect, such as a chance being Lucky causing it to be rolled twice and use the better result, or an effect skipping the roll entirely to force something to succeed or fail. The Effective chance is the real chance to get a specific result, accounting for all such roll-manipulating effects.

For example, if you had a Critical Hit chance of 20%, and your Critical Hit chance was Lucky, you would have an Effective Critical Hit chance of 36%, which is the chance that at least one of the two 20% rolls succeeds.