Walter Rodney said this quote
“ On any basic figure of the Africans landed alive in the Americas, one would have to make several extensions- starting with a calculation to cover mortality in transshipment. The Atlantic crossing, or “Middle Passage,” as it was called by European slavers, was notorious for the number of deaths incurred, averaging in the vicinity of 15-20 per cent. There were also numerous deaths in Africa between time of capture and time of embarkation, especially in cases where captives had to travel hundreds of miles to the coast. Most important of all (given that warfare was the principal means of obtaining captives) it is necessary to make some estimate of the number of people killed and injured so as to extract the millions who were taken alive and sound. The resultant figure would be many times the millions landed alive outside of Africa, and it is that figure which represents the number of Africans directly removed from the population and labor force of Africa because of the establishment of slave production by Europeans. Pg. 96 ”