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 "Joanna Jędrzejczyk"): She is the current UFC Women's Strawweight Champion and the third European (and only Polish) champion in UFC history after Bas Rutten in 1999 and Andrei Arlovski in 2005.
Relevant evidence: No