I updated my hair care article with two graphs showing the effects of shedding. Click on the link and scroll down to the section on "shedding".
Ed
One factor to consider in the shedding is that there are hairs around the transition area between scalp and other skin where hairs grow for a much shorter time. Those are going to be lost much more often. For example, mine that max out at six inches are going to fall out about seven times for every four foot strand that sheds at the end of the natural lifespan.
I'm not sure somebody would create a predictive model but the design would have to factor in the lifespan variety of hair regions on a sample head. Every hair falls at the end of the individual maximum growth plus resting phase before disconnecting. The odds of a specific hair dropping are not based on a shed rate but on the current length of that hair. If a man has trimmed hair he won't know what portion of that strand has been lost to cutting.
I'd love to see research studies on this because it is interesting stuff to know about. Neat site by the way, Ed. It makes a great introduction read and I'm saving the link for new growers.
Elizabeth