im no statistician.
but if you take the left third of the bell curve and call that "small", take the middle third of the curve and call it "average", and take the last third and say its "large"- then the "large" group that is above "average" would be 7.5%.
so 7.5% of men sampled are 7.25" or larger.
I think the chart is pretty accurate I just think that it showcases that while, yes, if you fall between 5-7 inches you are average...but notice how it skews large. And for some reason a 5 inch penis seems small to many people when a 6 inch penis is often considered very nice, a handful, and even "big." Statistically yes, a 5.5 inch penis fits into the average category, but when you slice the numbers another way....just before 6 inches you see that if you feel like being less than 6 is "small" then this data supports that view as well as does many people's perceptions.