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To: cs551@merlot.usc.edu
Subject: Re: standard deviation...
Date: Tue, 12 Sep 2006 17:22:15 -0700
From: william@bourbon.usc.edu
Someone pointed out that I have an error in the equation.
The last equal sign should be a minus sign. Therefore:
variance(X) = average(X^2) - average(X)^2
Sorry about the mistake.
--
Bill Cheng // bill.cheng@usc.edu
-----Original Message-----
Date: Tue, 12 Sep 2006 16:57:18 -0700
From: william@bourbon.usc.edu
To: cs551@merlot.usc.edu
Subject: standard deviation...
Hi,
Let X be something you are measuring. The square of the
standard deviation of X is called the variance of X. One
simple way to calculate the variance of X is:
variance(X) = average(X^2) = average(X)^2
where a^2 means a squared. To calculate average(X^2),
just pretend you are measuring Y which is simply X^2.
--
Bill Cheng // bill.cheng@usc.edu