IS Forum
Forum Index Register Members List Events Search Today's Posts Mark Forums Read Help

Go Back   International Skeptics Forum » General Topics » General Skepticism and The Paranormal
 


Welcome to the International Skeptics Forum, where we discuss skepticism, critical thinking, the paranormal and science in a friendly but lively way. You are currently viewing the forum as a guest, which means you are missing out on discussing matters that are of interest to you. Please consider registering so you can gain full use of the forum features and interact with other Members. Registration is simple, fast and free! Click here to register today.
Tags probability

Reply
Old 5th February 2010, 02:00 PM   #81
Anerystos
Muse
 
Join Date: Jun 2007
Posts: 839
Originally Posted by Dave Rogers View Post
Let me just think out loud for a moment about the cards.

You have a set of five cards. One is drawn, and you make a guess. Your chance of getting it right is 0.2. A second is drawn; if you know what the first one was, your chance of predicting the second is 0.25. Your chance of getting the third is 0.3º, the fourth is 0.5 and the fifth 1 (because you can eliminate the other four). I haven't done the arithmetic, and I'm not sure I can be bothered, but it seems to me that the expectation value is that you'll get about three right purely by guess and elimination. Is that what he meant?

Dave
The arithmetic has been done.

See Epstein, R A: The Theory of Gambling and Statistical Logic.

My memory is that the expected score is about 8.3 out of 25 (eg Zenner cards): the maths is beyond me, but simulation shows that it works.

If anyone wants the reference, I'll get it.

Last edited by Anerystos; 5th February 2010 at 02:05 PM. Reason: Clarity
Anerystos is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 5th February 2010, 02:03 PM   #82
carlitos
"más divertido"
 
carlitos's Avatar
 
Join Date: Jul 2009
Location: USA! USA!
Posts: 24,384
Just ask your classmates to prove it. Seems simple enough.

- Work out the math for 57% likelihood (of predicting Heads / Tails) based on standard distribution
- Make a few bets.
- Flip a coin and count.
- Profit!!
carlitos is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 5th February 2010, 04:51 PM   #83
Robin
Penultimate Amazing
 
Robin's Avatar
 
Join Date: Apr 2004
Posts: 14,971
Originally Posted by carlitos View Post
Just ask your classmates to prove it. Seems simple enough.

- Work out the math for 57% likelihood (of predicting Heads / Tails) based on standard distribution
- Make a few bets.
- Flip a coin and count.
- Profit!!
Yes, I think that is the way to go. Obviously the professor and the classmates have gotten the wrong end of the stick about something or other.

But my guess is that they would not agree to it. It is often embarrassing to admit you have been wrong about something like this.

I actually started flipping coins and guessing the result. By the time I got to 25 coins I had guessed 60% correctly and was half thinking maybe there was something in it after all.

But by the time I got to 50 coins I was back to 50% accuracy. I haven't done the maths, but I am guessing that even at 100 flips you might get as many as 57% correct guesses.
__________________
We all hate poverty, war, and injustice
Unlike the rest of you squares.

Tom Lehrer - Folk Song Army
Robin is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 5th February 2010, 04:57 PM   #84
Robin
Penultimate Amazing
 
Robin's Avatar
 
Join Date: Apr 2004
Posts: 14,971
I once claimed to my brother that there was a certain plant that was estimated to have lived since prehistoric times. When he challenged me I went to look for the research and found that I had simply misremembered and that the root system was estimated to have lived only since Roman times.

The great temptation was to simply say that I couldn't find the research and let the matter drop, especially since my brother has a habit of rubbing in silly mistakes like that.

In the end I 'fessed up about my mistake but it was a close decision.

I suspect the professor is in a similar position to this.
__________________
We all hate poverty, war, and injustice
Unlike the rest of you squares.

Tom Lehrer - Folk Song Army
Robin is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Old 5th February 2010, 05:02 PM   #85
GreyICE
Guest
 
Join Date: Mar 2008
Posts: 7,149
Originally Posted by Robin View Post
I once claimed to my brother that there was a certain plant that was estimated to have lived since prehistoric times. When he challenged me I went to look for the research and found that I had simply misremembered and that the root system was estimated to have lived only since Roman times.

The great temptation was to simply say that I couldn't find the research and let the matter drop, especially since my brother has a habit of rubbing in silly mistakes like that.

In the end I 'fessed up about my mistake but it was a close decision.

I suspect the professor is in a similar position to this.
Amusingly, you may have been right.

http://news.nationalgeographic.com/n...dest-tree.html

9,500 years is, if not prehistoric, close.

But it's a good story.
GreyICE is offline   Quote this post in a PM   Nominate this post for this month's language award Copy a direct link to this post Reply With Quote Back to Top
Reply

International Skeptics Forum » General Topics » General Skepticism and The Paranormal

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -7. The time now is 11:53 PM.
Powered by vBulletin. Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.

This forum began as part of the James Randi Education Foundation (JREF). However, the forum now exists as
an independent entity with no affiliation with or endorsement by the JREF, including the section in reference to "JREF" topics.

Disclaimer: Messages posted in the Forum are solely the opinion of their authors.