Let's say for every 100 normal people there is 1 witch, in other words 1:100. Going by that and saying the world has hmmm ~=8,000,000,000 people that would mean there are 80,000,000 witches. If there is a 1:1000 ratio of wizards then that would mean there are in the world =~ 80,000 wizards. And if the ratio of dark witches is 1:20,000 then 80,000,000/20,000= 4,000 dark witches meaning that there is a 0.005% chance for a dark witch to appear. Well that sure looks like a percentage for an SR witch...wait no, light witches are 1:10,000 so they would be R witches...yeah it's right then calling the dark witches SR meaning the spirits would be UR then since they are 1:100,000. (Correct me if I'm wrong or if I'm exaggerating.)