Scientists are often blinded by attempts to prove preconceived theories. When objectivity is lost bad science is the result. At times these theories are very unpopular such as this one. Others such as the causes of global warming seem to be much more readily accepted, but are given birth by the same wish to prove a theory by ignoring contradicting data.
To often there is a desire to expound beyond what can be or not be proven. When we try to average a large group and compare that to the average of another large group results may be not at all as they appear.
Perhaps starvation and disease may keep one group lower than the other even though the upper percentage of the lower group may exceed the same upper percentage of the higher one. This proves nothing! I can statistically prove that the most deadly places are hospitals by showing that more people die there than most other places.
Figures don't lie but liars figure.