I've noticed that the most common transposition error for me is when a word ends in a left-handed key, I switch it with the following space, which I type with my right hand, particularly if the word ends in a 't' or an 'a'. I guess I'd do it with 'z' and 'q' also, but words that end with those letters are rare. Fairly often I erroneously repeat a 't' after the space after a word that ends in 't' (e.g. "that thas").
I would be very surprised to see transposed letters that are on the same hand. I managed to produce a "teh" and a "hadn" while typing the last sentence (and just now a "whiel") but would be surprised to produce a "surprisde" unless I had recently acquired alien hand syndrome.
But my "inner loop" seems to be aware of many of these errors because I'll often correct them even if I can't see what I'm typing.
