I do mean any statistics -- some controlled experiments, sieving through surveys, anything. I'm constantly being told old wives' tales by friends and old doctors' tales by doctors. I'm not asking for well-done science here, just if anybody has investigated anything at all -- any data. Not a duplicate.
I'm not finding anything recent. I think Rory Alsop is probably correct about it being a "legacy guidance". If your baby is already nursing well, I wouldn't worry about using a bottle at all. If this is still a concern for you, (I see the date of your post was back in May) you can generally trust the pediatrician to have the most up-to-date answers for you. Also, Nipple confusion is one of those things we all get warned against, but then it doesn't happen all that often anyway. I nannied for a young man that had trouble with it though. It wasn't that big of a deal though, because she could still pump and he was still getting the nutrients when it was given to him from a bottle - plus Dad could participate more. It might be disappointing for the mother if that happened but it isn't going to mean the difference between life and death or even success or non-success later in life.