math guys: how does one figure out a standard deviation

[self biased]

it's been ages since i've had to use this, but i was wondering how to apply this to a game we play that involves rolling many, many dice.

[Asher]

1. excel
2. stdev([cell range])

[self biased]

unfortunately i don't have access to a laptop when i'm playing a game. i need to be able to figure out if a set of rolls is within one or not more or less on the fly.

[Lawrence of Arabia]

find the mean
then find the variance
then take the square root of the variance.

[Lawrence of Arabia]

i dont see how you can apply this to a game of rolling the dice many times. since the expected value of each roll is 3.5, an infinite number of rolls will lead to a standard deviation of zero (by Central Limit Theorem)
similarly, a large number of rolls (say 100) will also get you a standard deviation that will approach zero (by Law of Large Numbers)

[KrazyHorse]

The population standard deviation can be simply calculated as follows:

1) sum all values
2) sum the squares of all values
3) square the result from (1)
4) Divide (3) by N (the number of values)
5) Subtract (4) from (2)
6) Divide (5) by N
7) Take the square root of (6)

So, if we have 3, 6, and 7 as values:

1) = 3+6+7 = 16
2) = 9 + 36 + 49 = 94
3) = 16*16 = 256
4) = 256/3 = 85.33
5) = 94 - 85.33 = 8.67
6) = 8.67/3 = 2.89
7) = SQRT(2.89) = 1.7

[KrazyHorse]

Originally posted by Lawrence of Arabia
i dont see how you can apply this to a game of rolling the dice many times. since the expected value of each roll is 3.5, an infinite number of rolls will lead to a standard deviation of zero (by Central Limit Theorem)

Uhhhh....no

[Lawrence of Arabia]

uuuuh yeah.

SE = Stdev/sqrt(n)

[KrazyHorse]

Would you like to make any more absurd statements about basic statistical concepts, Lawrence?

[KrazyHorse]

Originally posted by Lawrence of Arabia
uuuuh yeah.

SE = Stdev/sqrt(n)

You must be an idiot...

[Lawrence of Arabia]

must be . . .

[Lawrence of Arabia]

oh, one more thing. you proved my point in your previous post

6) Divide (5) by N
7) Take the square root of (6)

what happens when n=100. when n= 1000? when n= 10000

[KrazyHorse]

Let's make this absolutely clear: you are claiming that the standard deviation of any set of independent dice rolls approaches 0 as the size of the set approaches infinity?

[KrazyHorse]

Originally posted by Lawrence of Arabia
oh, one more thing. you proved my point in your previous post

6) Divide (5) by N
7) Take the square root of (6)

what happens when n=100. when n= 1000? when n= 10000

What happens is that the difference in the sums grows linearly, you idiot.

[KrazyHorse]

Do all economists receive such a poor education in statistics, or are you particularly dimwitted?