Sunday, May 01, 2005

Dodgy mathematics

Though I have my doubts about the official 9/11 account, this is not the way to go about debunking it. Here is a simple refutation of the article's premise:

Assume that a murder has taken place and that the prosecution asserts that:

A. The defendant bought a knife at a store.
B. The defendant stabbed the victim with this knife.

If it can be shown that the defendant didn't buy the knife at said store, then the assertion that the defendant bought the knife at said store AND stabbed the victim with this knife is false, which is a perfectly valid assertion. But this does not prove that the defendant did not stab the victim with that knife.

Similarly, if the probability of the defendant buying the knife at a particular store being true is 0.1 and that of his stabbing the defendant with it being true is 0.7, the probability of both these assertions being true is 0.1 x 0.7 = 0.07; again, a valid statement. But this still does not make assertion B any less likely, or preclude another high-probability compound event (example: the defendant stole the knife [probability 0.4] and stabbed the victim with it [probability 0.7] -- leading to a compound probability of 0.4 x 0.7 = 0.28).