I believe that they did look at crimes like murder and assault as a control for sex crimes in at least some cases.

I did hear of a study once (no, I don't have a citation) tracking US sex crime rates in relation to when the internet (broadband?) became widely available in different parts of the country, finding some tendency for rape to go down after the internet was available.

In any case, those are all helpful ideas for professional sex researchers but go beyond my competence.