On no, this thread has made a comeback again, with it's inaccurate information. Reputable scientific studies show no appreciable average penis size differences between various countries or ethnicities. For instance a scientific study done in Nigeria showed an average size 0.2 inches smaller than a scientific study done in South Korea. Nearly every scientific penis size study has found an average erect length between 5.1 and 5.5 inches bone pressed and an average erect girth between 4.5 and 4.7 inches taken at the mid-point of the shaft. Even those averages may be larger than the true average, due to the potential reluctance of smaller men to have their penises measured by medical staff, whereas a larger man might be more willing to show up for the study in order to show off.
The average human penis is nowhere near as large as people expect it is. Any survey that relies on self reporting ends up biased by factors like perceived ideal size (which is often skewed by pornography) and trolling. Studies show that most people think the average penis size is larger than it is, with most people thinking the average is between 6 and 6.5 inches, but the Brazilian Journal of Urology actually compiled the data from 17 scientific penis size studies from around the world, what they found is that only 5 out of 100 men have a penis longer than 6.3 inches.
There is also a general belief that women prefer larger penises than they actually do. There was a study done where they 3D printed various penis like dildos with no measurements written on them and asked women to pick up the one they found to be the ideal size for a one night stand and the one they found to be the ideal size for a long term relationship. The average of the casual sex penis was 6.4 inches long by 5 inches girth, while the average of the long term relationship penis was slightly smaller at 6.3 inches long by 4.8 inches girth. While both are larger than the average man, it's not a huge difference and the ideal is certainly not the 8 inch by 6 inch meat bat that watching pornography would make you think the majority of women like.
Yup, studies like these (in the OP) are often funded by porn companies to promote BBC porn and the like.