## probability math

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• I recently read about an astrologer who was asked to write horoscopes for 12 unidentified people, meet those 12 people, and then guess which was which. The
Message 1 of 2 , Feb 8, 2002
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for 12 unidentified people, meet those 12 people, and then guess
which was which.
The astrologer didn't make a single correct guess.

That surprised me, because I thought that the chances were greater
than 50% in favor of getting at least one correct guess.

But I think I was wrong. I began calculating the formula for the
chances of getting at least one correct match given the number of
people being matched. Here's what I came up with:

Given 1 person, the chances are 1 out of 1.
Given 2 persons, the chances are 1 out of 2.
Given 3 persons, the chances are 4 out of 6.
Given 4 persons, the chances are 6 out of 16.

And that's as far as I figured.
I can't discern a pattern from this data, and it would be quite
laborious to figure out the chances given 5 persons.
Does anything already know what the formula is?
Or does anything see a formula from this data?

Thomas Robertson
http://www.pentatonika.com
• Thomas, actually some paranormalists have tried to get credit for reverse hits when they appear to get far below normal chance. It utterly amazes me that so
Message 2 of 2 , Feb 9, 2002
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Thomas,

actually some paranormalists have tried to get credit for "reverse hits" when they
appear to get far below normal chance. It utterly amazes me that so many people
believe in astrology when it is so simple to disprove. Culver and Ianna wrote the
one of the only good (read skeptical) book on astrology out there.

I'm bcc-ing a high school student who has some interest in taking on a
senior project to investigate paranormal claims. I personally think the math
of looking for above chance probabilities of hits could be fascinating.
Probability does sometimes appear to violate ones intuitive sense. If I were
testing astrology, I'd probably try to have people pick which of only 4 charts
were heir's. I'd also take care to try to filter out subjects who already closely
followed their charts. Realize that if you disproved one astrologer, others would
say you used the wrong method. I offer a lot more ramblings on astrology at:
http://www.phact.org/e/astrolgy.htm

Eric Krieg
----- Original Message -----
From: "pentatonika2000" <pentatonika@...>
To: <skeptical@yahoogroups.com>
Sent: Saturday, February 09, 2002 1:54 AM
Subject: [skeptical] probability math

>
> for 12 unidentified people, meet those 12 people, and then guess
> which was which.
> The astrologer didn't make a single correct guess.
>
> That surprised me, because I thought that the chances were greater
> than 50% in favor of getting at least one correct guess.
>
> But I think I was wrong. I began calculating the formula for the
> chances of getting at least one correct match given the number of
> people being matched. Here's what I came up with:
>
> Given 1 person, the chances are 1 out of 1.
> Given 2 persons, the chances are 1 out of 2.
> Given 3 persons, the chances are 4 out of 6.
> Given 4 persons, the chances are 6 out of 16.
>
> And that's as far as I figured.
> I can't discern a pattern from this data, and it would be quite
> laborious to figure out the chances given 5 persons.
> Does anything already know what the formula is?
> Or does anything see a formula from this data?
> If so, please write back.
>
> Thomas Robertson
> http://www.pentatonika.com
>
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>
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