Question: What is the ranking system used in combat sports, including boxing and mixed martial arts, of who the better fighters are relative to their weight, by which measure the Polish mixed martial artist Joanna Jędrzejczyk is rated the number 1 female MMA fighter in the world?
Sentence (from "Skip Hall (MMA)"): He was a participant in the Jasper City Slugfest in August 2006 against former UFC Superfight Champion Dan Severn, and retired in 2009 from active MMA fighting after declaring himself "Oldest Active MMA Fighter in history."
Relevant evidence: No