The main source was the avi chai foundation study of class sizes for all day schools in North America. The results have been corroborated by other studies. I am not an actuary and was not invlolved in discovering the problem although I have seen the studies. I think mox mentioned earlier that he did some of the research. Perhaps he will enlighten us as to the rest of the source material.
Truth be told, one does not need to be a mathematician to realize that B”H our population is growing very rapidly. One also does not need to be a mathematician to realize that girls start dating around 19 and boys around 22. What obviously follows is that there is certainly not enough 22 yr old boys for the 19 yr old girls. Perhaps one need to be a mathematician to figure out if the discrepancy is 9.67% or 11.13% or somewhere in the middle. From my point of view either way it’s an unacceptable problem and something we must do our utmost to alleviate.