Suicide Junkie and Parasite,
Thank you. I rolled your suggestions into my original post.
Bearclaw,
Your idea sounds quite interesting. However, it sounds like it's the beginning of an entirely new and complex model... perhaps I'll add it as an addendum as an idea for a different model?
By all means if anyone has any ideas on improving the model I propose... or proposing any models of their own, please do. Or if their are any great ideas I missed from a previous thread...