This is very interesting, Dr Bill, and I have no idea if it's possible or not to approximate these things. We'll have to count on our technical advisors.

One thing Faldage has noticed and pointed out to me is that the newcomers who stay are usually ones whose first post is a contribution to a discussion already in progress. Those who post a question in Q&A are as often as not one-time apparitions (Faldage, correct me if I'm wrong and I know you will!).