Most of it is, but not all of it. My own conclusion (which is not the one I wanted to reach, believe me) was that when you throw out all the bad research, the evidence, while not conclusive, does clearly point more in one direction than the other.
The major studies that have been done are fairly easy to find with some google investigation. I looked at them all over a year ago and formed my conclusions. I unfortunately didn't keep around a list of links to post in debates on internet forums.