>>10866478The African countries on that chart are self reported. Here's a real study
Objective: Amongst the Caucasians and some non-Black races, there is the popular belief that the black people generally have longer penile sizes. Even the Blacks themselves tend to believe so. This study was carried out to test the veracity of this ascription of “oversized” penile length to people of the Black (Negro) race. Design: A prospective and comparative study Setting: The Nnamdi Azikiwe University Teaching Hospital, Nnewi, Nigeria. Subjects and Method: Full-stretch flaccid penile lengths, and flaccid penile lengths, were measured in 115 adult men of the Black race in Nigeria. The results were compared with reported similar main studies on people of other races, which were accessible to the authors. These studies were done in Italy, Greece, Korea, Britain, and the United States of America. Result: The mean full-stretch penile length of the Nigerian Blacks was 13.37cm and the mean flaccid length was 9.36cm. Similar studies reported full-stretch penile lengths of 12.50cm in Italians, 12.18cm in Greeks, 9.6cm in Koreans, 13cm in British Caucasians, and 12.45cm in the American Caucasians. The penile length for Nigerian Blacks was longer than those of the other races, but the differences were only statistically different in comparison with the Koreans. Conclusion: There is the possibility of racial differences in penile sizes, but there is no convincing scientific background to support the ascription of bigger penile dimensions to people of the Black race
https://www.ajol.info/index.php/tjmr/article/view/30465 
