http://www.ces.ncsu.edu/depts/fcs/pdfs/fcs_504.pdf
http://www.cec.sped.org/AM/Template.cfmSection=Search&template=/CM/HTMLDisplay.cfm&ContentID=2701
http://www.umext.maine.edu/onlinepubs/pdfpubs/4358.pdf
http://www.bianys.org/learnet/tutorials/aggression.html