You need to perform an intervention to test for correlation vs. causation, and that would involve getting lots of normal children, and traumatising half of them. Those studies are considered a bit retro in the scientific community, for some reason.
http://www.danielpearl.org/about_us/Judea_Pearl.html
http://ftp.cs.ucla.edu/pub/stat_ser/R320.pdf
The usual link to Peter Norvig (director of research at Google) on experimental research, which is good food for thought:
Edit: Okay - I clearly have to clarify my comment. Intervention studies are not retro. Studies in which you deliberately traumatise children, however, went out with Ceacescu. I was making a joke (albeit apparently a poor one).