You didn't get many love notes in high school, did you, Joe?
Okay, neither did I. But the one(s) I did get were written in the same handwriting. And I have five sisters and two of them write just like other girls I know. The other three are all artsy and shit so that doesn't count. Just like my wife.
But seriously... I have no proof... and maybe I was over-shooting with the 99.9% thing, but its at least 75%.
There needs to be some serious research in this area.