The phrase "disproportionate number" means that there is an unequal or unfair amount of something compared to what is expected or considered normal. Full definition
The studies found that grossly disproportionate numbers of minority students are identified as eligible for services, and too often placed in isolated and restrictive educational settings. (gse.harvard.edu)
They fought and died in disproportionate numbers in a racist war that defended elite class interests. (religion-online.org)
In the womb, boys produce twice as much testosterone as girls, providing possible clues as to why autism strikes males in such disproportionate numbers. (discovermagazine.com)