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"): Joanna Jędrzejczyk (] ; born August 18, 1987) is a Polish mixed martial artist and former Muay Thai kickboxer who competes in the women's strawweight division of the Ultimate Fighting Championship.
Relevant evidence: Yes