The following letter was sent to me in response to my column in Scientific American (which generated hundreds of letters in response, so I penned the following response) in which I discussed the now-infamous (and infuriatingly counter-intuitive) probability problem called the Monty Hall Problem, or the Three Door Problem, in which a contestant chooses one of three doors, behind one of which is a car and the other two goats. Monty then reveals what’s behind one of the other doors (only ever showing a goat and never showing you your own door pick), which is always a goat, then asks if you want to change doors. Most people say it doesn’t matter because now it’s 50/50, but the correct answer is that you should always switch, which will give you a two-thirds chance of winning. There are simulations of the game online, but my correspondent took it upon himself to test the game with his own computer program. Here are his very interesting results, which also nicely show the scientific method at work: (continue reading…)

The Law of Large Numbers guarantees that one-in-a-million miracles happen 295 times a day in America

Because I am often introduced as a “professional skeptic,” people feel compelled to challenge me with stories about highly improbable events. The implication is that if I cannot offer a satisfactory natural explanation for that particular event, the general principle of supernaturalism is preserved. A common story is the one about having a dream or thought about the death of a friend or relative and then receiving a phone call five minutes later about the unexpected death of that very person.

I cannot always explain such specific incidents, but a principle of probability called the Law of Large Numbers shows that an event with a low probability of occurrence in a small number of trials has a high probability of occurrence in a large number of trials. Events with million-to-one odds happen 295 times a day in America. (continue reading…)