I don't know how one could do "research" or study it as no one is going to come forward as they are doing such acts? All one has is someone's memory of what they believed happened to them years before. I think it would be very hard for all the people involved to all be continuously doing this to children and no one else learn of it and "catch" them in the act (like they catch moonshine makers). Where there's smoke there is often fire but no one has seen any actual smoke.

I think something as horrendous as what is described could not continue for so long without someone being caught, something being collaborated and everyone hearing about it in the mainstream news, etc.