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Subject: Re: Prob of getting the expected value exactly is not always high...

Author: Michael Yee

Date: 14:04:48 10/12/04

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On October 12, 2004 at 10:28:16, Graham Laight wrote:

[snip]

>How does one explain such a poor performance by Junior, which had massively
>superior hardware to Fritz?  Should we ask the Junior programmers to forward
>their program to to Franz Morsch for advice and improvement?
>
>-g

If the variance of a random variable is low, maybe then you could expect the
outcome to be close to the expected value most times. But it's not true in
general. For instance, consider the experiment of 3 flips of a binary coin
(0/1). The 8 possible outcomes are:

000
001
010
011
100
101
110
111

Some probabilities of getting n flips:

P(0 flips) = 1/8
P(1 flip ) = 3/8
P(2 flips) = 3/8
P(3 flips) = 1/8

Notice in this case that P(E[x] = 1.5 flips) = 0! (That is, it's impossible to
get the expected value in this case in one run of the experiment.)

Also note that P(< 1.5 flips) = 0.5 (since the distribution is symmetric).

To bring this back to the bilbao results... I would just say that to expect
Junior to consistently play at a certain level (say 8/10, 8/10, 8/10, etc.) is
asking too much. In fact, maybe Junior's style of play introduces more variance
over short runs (6/10, 10/10, 8/10).

Michael



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