== Major Revision == 
 On September 12-13, 2010, this page underwent major revisions as part of a postgraduate academic assignment linked to making a contribution to Wikipedia in the area of decision making.  In several instances, the original content on the page was unreferenced or sparsely referenced.  That problem was rectified where possible.  The largest remaining challenge is in the area of Types, and specifically sub-types.  The information in that sub-section of the page comes from questionable sources or is not referenced.  Recommend a notice be placed above that section by Wikipedia editors with the ability to do that.  This revision included structural changes, content additions, reference additions, and grammatical and punctuation corrections.