[net.math] simple statistics question

ka@hou3c.UUCP (11/30/83)

Periodicly I see arguments like, "Deterrence has kept the peace for 35
years, which proves the probability of deterrence failing is low."  What
I am wondering is just how low the "low" probability is (assuming for
the sake of simplicity that this  probability does not change over time).

This problem can be recast in terms of balls and urns.  Assume that I
have an urn containing an essentially infinite number of green and/or
red balls.  If I draw 10 balls from the urn and all of them are red,
what is the probability that the next ball drawn will be red?
				Kenneth Almquist

hon@ihuxv.UUCP (Herb Norton) (11/30/83)

I have seen the solution to this type of problem given as:
if you have observed an the same outcome in N trials the
probability of not observing that outcome in the next trial
is 1/(N+1).  This is intuitively resonable since if you do
observe  the different outcome on the N+1st trial then you
have observed it once in N+1 trials which is just the probablity
you assigned.  If you don't observe a different outcome, it is
still what you expect since that the different outcome had
low probability.
				Herb Norton

colonel@sunybcs.UUCP (George Sicherman) (12/04/83)

The balls-and-urns analogy is a little misleading.  If deterrence
fails, it will probably do so only once.  The "event" is thus not
repeatable.
			George Sicherman
			...seismo!rochester!rocksvax!sunybcs!colonel