Comments on: The coin toss: not 50-50 after all

By: gneo

gneo — Thu, 29 Oct 2009 07:11:30 +0000

And:

http://www.mrexcel.com/forum/showpost.php?s=c1d4a66967bc033c04455a577f5effd0&p=16238&postcount=2

By: gneo

gneo — Thu, 29 Oct 2009 07:09:26 +0000

“Random numbers are based on a predictable algorithm. If you know the previous number and the algorithm, you can predict the next number(s) generated by the random function. This sounds counter-intuitive, but that’s because random numbers which are generated by computers are not truly random. [...] You can test this for yourself. [...]”

http://www.mrexcel.com/forum/showpost.php?p=391514&postcount=7

By: Anonymous

Anonymous — Tue, 27 Oct 2009 15:43:01 +0000

At least we could *once* have taken some comfort from the eminently plausible proposition that the side of the coin facing up at the start of the flip was independent of anything that mattered.

But now that you’ve brought this to the attention of the coin flippers, there goes that too. Thanks alot, guys. Now I gotta go out and find only illiterate coin flippers who have no friends who read statistical computing blogs. Where on *earth* am I supposed to find *them*?

By: How to flip a coin « Free Market Mojo

How to flip a coin « Free Market Mojo — Mon, 26 Oct 2009 09:26:20 +0000

[...] to flip a coin Chris Blattman writes: Using a high-speed camera that photographed people flipping coins, the three researchers [...]

By: Etl World News | How to flip a coin

Etl World News | How to flip a coin — Mon, 26 Oct 2009 02:18:07 +0000

[...] Blattman reports: Using a high-speed camera that photographed people flipping coins, the three researchers [...]

By: David

David — Sun, 25 Oct 2009 16:24:41 +0000

Manoel,

Well, yeah. Heads – Tails will approximately distributed as Normal( 0 , t/2) after t trials, which goes to infinity in both directions as t gets large

. But the actual proportion Heads/(Heads+Tails) will go to Normal(1/2, 1/(4*t)), which should tend to 1/2 pretty quickly. The only way you’d see divergence is if the probability is truely something else other then 1/2.

By: Manoel Galdino

Manoel Galdino — Sun, 25 Oct 2009 13:42:50 +0000

You can’t randomize using an deterministic algorithm. So, if you use a very long series of numbers generated in excel, at some (long) time you will see a pattern. Look here:
http://en.wikipedia.org/wiki/Pseudorandom_number_generator
But this is not a concern for short series (say, one hundred thousand numbers, even one million numbers).

I didn’t see the paper, but I do not think this is a suprise. You should google “random walk first return”. It is a well established result in stochastic process that if you flip a coin, say, 10000 times, most of time it will show one of the sides leading (ie. more landing of one side than the other). A very good discussion you can find in the famous Feller’s book. ( An Introduction to Probability Theory and Its Applications)

By: coozzle

coozzle — Sun, 25 Oct 2009 08:01:18 +0000

Not just excel, any programmed random function is just pseudo random at best…
one of the key differentiators between humans and machines is the inherent randomness of human character. Excel just uses a timestamp based seed to generate a combination from around 2E11 possibilities…

By: A

Sun, 25 Oct 2009 06:31:11 +0000

Real randomistas randomize with stata – are we in the clear?

By: Keith

Keith — Sun, 25 Oct 2009 04:59:15 +0000

http://www.pages.drexel.edu/~bdm25/excel-rng.pdf