> Even when given explanations, simulations, and formal mathematical proofs, many people still do not accept that switching is the best strategy (vos Savant 1991a). Paul Erdős, one of the most prolific mathematicians in history, remained unconvinced until he was shown a computer simulation demonstrating the predicted result (Vazsonyi 1999).
It's such a deceptively simple problem that's so easy to get wrong. I introduced it to my boss and he just wouldn't believe me when I told him the answer. He spent about 10 minutes formulating a simulation in Excel in order to convince himself.
I remember writing a JavaScript simulation to convince myself :)
I think the reason why problem is so unintuitive is some subtleties in how the problem is posed.
Monty does not just open a random door:
- He always opens one of the two doors you didn't choose.
- He knows where the prize is beforehand, and deliberately open a door which doesn't contain the price.
It should be stated clearly that these are the rules Monty follows. If the problem is stated like he just randomly decides to open one of the doors, then you can't say anything about how it affects the chances.
The citation on the wikipedia page does not really makes these rules explicit. It states
> the host, who knows what's behind the doors, opens another door, say No. 3, which has a goat.
It is not really clear from this that the host are following the above stated rules. It is not stated explicitly that the host couldn't have chosen the door selected by the contestant, just that he didn't. If you don't know what rules he is following in selecting a door, then his door selection does not really give you more information. Stating the problem like this it is bordering on a trick question.
All totally true, but the interesting thing is that even when they made those same assumptions (which seem to me, at least, the most reasonable assumptions), people - including the PhDs - still assessed the probabilities incorrectly.
The really difficult thing to get your head around is that the door you chose still has a 1/3 probability, despite the fact that you know there are two doors, one of which hides the car, and the other hides the goat.
switching is not optimal if you give Monty the option to not propose a switch. In this case you must consider the possibility that Monty is only offering me a switch because I have currently picked the winning door.
> The show’s producers showed mercy on the “zonk” winners, however. After the taping of the show, they would be offered a substitute prize, such as a television, and most would take it. “In 1 percent of the cases, they didn‘t,” Hall said. “There was a time when a farmer won five calves and he wanted the calves. That cost me a fortune because when you rent them from the animal place, they’re expensive.”
- https://twitter.com/ATabarrok/status/914318431297708032