
10/17/2002, 04:26 PM
#214
Originally posted by KRamsauer
Not knowing who that character was, I went searching. I came across the following, linked to from a site that shows all examples of her being wrong:
http://www.dartmouth.edu/~chance/cou...onty_Hall.html
Some highlights (emphasis added):
" Mr. Hall said he realized the contestants were wrong, because the odds on Door 1
were still only 1 in 3 even after he opened another door. Since the only other place
the car could be was behind Door 2, the odds on that door must now be 2 in 3. "
" "So her answer's right: you should switch," Mr. Hall said, reaching the same
conclusion as the tens of thousands of students who conducted similar
experiments at Ms. vos Savant's suggestion. That conclusion was also reached
eventually by many of her critics in academia, although most did not bother to
write letters of retraction. Dr. Sachs, whose letter was published in her
column, was one of the few with the grace to concede his mistake.
"I wrote her another letter," Dr. Sachs said last week, "telling her that
after removing my foot from my mouth I'm now eating humble pie. I vowed as
penance to answer all the people who wrote to castigate me. It's been an intense
professional embarrassment.""
" The results contradict most people's intution that, when there are only two
unopened doors left, the odds on each one must be 1/2. But the fact that Mr.
Hall opens another door doesn't affect the odds on Door 1: You had a onethird
chance of being right to begin with, and you still have a onethird chance after
he opens, say, Door 3. You knew he was going to open another door and reveal a
goat regardless of what was behind Door 1, so his action provides no new
information about Door 1. Therefore, since the odds on Door 1 are still
onethird, and the only other place the car could be is behind Door 2, the odds
on Door 2 must now be twothirds. "
And all of that is irrelevant because Monty was not required to offer a switch. To quote Monty himself, "If the host is required to open a door all the time and offer you a switch, then you should take the switch," he said. "But if he has the choice whether to allow a switch or not, beware. Caveat emptor. It all depends on his mood."


