Cousin couple genetic disorder?

This is just somebodies statistics. How they did it was to look at the results of a group of non related people and did the likeliness of a genetic disease. Then they did the same with a group of the same amount of people that were related this way and compared the two. The answer was 13 times more likely that the couple that was related would have children with a genetic disease then the couple that had no relationship. I hope this helps explain it better. Good luck and God Bless