By definition SIDS is a sudden, unexplained death of a child less than one year old. So if the cause is unknown, why such the strong push to have children sleep on their backs? Statistics show that since the massive 'back to sleep' effort has started SIDS deaths are down, but I also am aware that statistics can be misleading. One of my college roommates even had a class on how to make statistics lie.
I think that placing a child on his or her back to sleep works because of the other dangers that it mitigates, not necessarily just because the child is on their back. Even though I know statistics can be misleading, as stated earlier, I would be very interested in seeing the numbers on other factors such as smoking, mattress firmness, room temperature, and mattress pad thickness. I would hazard a guess that there would be a correlation between the additional factors and the occurrence of SIDS… apart from the child simply being on his or her stomach. All of these factors are listed in the NISP survey, but I can't seem to find the numbers. Maybe I just suck at google.
Since my wife and I have eliminated the other risk factors, we have no problem letting the little one sleep on her stomach. However, I know I am biased because of my experience with the three year old, and having to fit her with a DOC band (watch for some posts on DOC bands!) to correct the shape of her head, so please, make sure to carefully do your own research and don't just take my word for it. You have to do what you think is right. I'm just some dude with a blog and an opinion, not a doctor.