Approxamately what percentage of the entire securities market is
invested in pensions, mutual funds, and retirement investment
accounts? I will be happy with an answer that shows an experts best
guess since I imagine that a number like this would be difficult to
pinpoint.

http://www.ici.org/pdf/99fb_ch6.pdf
This site tells you a lot of info on these catagories and the
percentile of holdings in each.  Good luck with your research
Professor.  I hope that this helps you