Brian, Sorry if I appeared to be attacking your arguments when I raised the question of when exactly is refered to by the phrase "when the symptoms show". Actually I was not thinking of your ideas at all, merely raising the matter in its own right. You wrote: > Only those specialists who have actually dissected a brain, applied dyes > to the samples and observed the result, can talk meaningfully in terms of > absolute values. There is no way that I, as an Engineer can communicate on > that level, but I can try to express my ideas in the form of these models, > and thereby create something which those less technically inclined can > understand and apply to get a better grasp of the subject under review. My own background in meteorology, the army and management has also failed to turn me into an M.D.(I'm still trying to work out why not), though I can usually manage to follow a line of reasoning despite this setback. BTW, one branch of my family has Engineers in abundance, including a Professor and a Ph.D. They are wonderful people, great company and build beautiful bridges, but have shown no more medical ability than any other non medics. Sadly it seems competance, or even brilliance, in one speciality conferes no status or special knowledge in an unrelated field. Which is a great pity because it means that my rather extensive knowledge of W.B.Yeats and T.S.Eliot will never be much good for more than tacking appropriate quotes at the end of letters. In this case, in honour of all the questing minds on this list, I thought the following extract from Eliot might be fitting: "We shall not cease from exploration And the end of all our exploring Will be to arrive where we started And know the place for the first time." Dennis. ************************************************** Dennis Greene 48/11 [log in to unmask] http://members.networx.net.au/~dennisg/ **************************************************