Ah, I read this article in one of the AACN magazines. There was actually more to the study than is listed that this article does not report. What they were actually trying to do is link patient outcomes to nursing certifications which was a FAIL. It appears that certifications don't do a damn thing for the patients -- but they do for the nurse (weak association at that.)
Most of the outcomes that the AACN/ANCC has tried to research to back up it's programs hasn't been all that successful.