Listen to that stat at the end of this video.
Someone also wrote a book on this topic: http://amzn.to/2tXVRUm
(Side note: This single video was what inspired us to create Unstripped Voice in summer 2016. Our founder saw this footage on a facebook friend’s page and never heard of this…and assumed not many others did either. So he created the Unstripped Voice facebook page to post this and many other videos to enlighten minds on Black history they didn’t teach in schools).