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?

<P0-S0>  As these fighters do not compete directly, judging the best fighter pound for pound is subjective, and ratings vary. <P0-S1>  They may be based on a range of criteria including "quality of opposition", factors such as how exciting the fighter is or how famous they are, or be an attempt to determine who would win if all those ranked were the same size. <P0-S2>  In boxing, the term was historically associated with fighters such as Benny Leonard and Sugar Ray Robinson who were widely considered to be the most skilled fighters of their day, to distinguish them from the generally more popular (and better compensated) heavyweight champions. <P0-S3>  Since 1990, "The Ring" magazine has maintained a pound for pound rank of fighters. <P0-S4>  ESPN.com has a list for mixed martial artists. <P0-S5> Pound for pound is a ranking used in combat sports, such as boxing or mixed martial arts, of who the better fighters are relative to their weight (i.e., adjusted to compensate for weight class). <P0-S6>  In December 2013, Ronda Rousey became the first woman to appear on the top 10 of a mixed-gender major publication. <SEP> <P1-S0> Guy Mezger (born January 1, 1968) is an American martial artist, who competed in professional combat sports including full contact karate, kickboxing, and boxing, but is most recognized as a mixed martial arts (MMA) fighter. <P1-S1>  Mezger retired from professional competition on January 25, 2005. <P1-S2>  He is associated with Lion's Den and runs their school in Dallas. <P1-S3>  Mezger was a champion in mixed martial arts in two different promotions, the UFC and Pancrase. <P1-S4>  He holds wins over Tito Ortiz, Masakatsu Funaki, Yuki Kondo, Semmy Schilt, and Minoru Suzuki. <SEP> <P2-S0> 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. <P2-S1>  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. <P2-S2>  As of May 2017, she is the consensus #1 female strawweight, and #1 pound-for-pound female MMA fighter in the world. <P2-S3>  She is also currently the #8 pound-for-pound fighter in the UFC mixed gender rankings, making her the top female on the list. <SEP> <P3-S0> Katja Kankaanpää (] , born June 30, 1981) is a Finnish former mixed martial artist who competed in the strawweight division. <P3-S1>  She is currently signed with Invicta FC. <P3-S2>  Kankaanpää started martial arts training at her teens when she was 15 years old with Goju-ryu karate. <P3-S3>  Later she had interest about combat sports by training submission wrestling and other combat arts. <P3-S4>  Katja leads the Nordic (all Skandinavia) strawweight rankings and Finnish women, all weight classes MMA rankings. <P3-S5>  On January 2, 2015 she was awarded 'Nordic Female Fighter of the Year'. <P3-S6>  The same month, Finnish sports journalists honored her as 'Sportswoman of 2014', category MMA.