Suppose you’re on a game show, and you’re given a choice between three doors, One has a car, one has a goat, and one has a tiger. You pick a door, and you figure it has 1⁄3 chance of having the car. The host tells you to stand in front of your chosen door. He presses a button, and one of the doors you didn’t choose swings open and a tiger jumps out. Should you update your previous belief that the door you chose has a 1⁄3 chance of having the car? Your only new evidence was that you’ve seen that the door you chose didn’t have the tiger. But if the door had had the tiger, you wouldn’t have seen that evidence, because the tiger would have killed you.
Suppose you’re on a game show, and you’re given a choice between three doors, One has a car, one has a goat, and one has a tiger. You pick a door, and you figure it has 1⁄3 chance of having the car. The host tells you to stand in front of your chosen door. He presses a button, and one of the doors you didn’t choose swings open and a tiger jumps out. Should you update your previous belief that the door you chose has a 1⁄3 chance of having the car? Your only new evidence was that you’ve seen that the door you chose didn’t have the tiger. But if the door had had the tiger, you wouldn’t have seen that evidence, because the tiger would have killed you.
Yes. The door now has a 1⁄2 chance of having the car.
(This is assuming that the host’s button means “open the door with the tiger”.)