Re: Difference b/w Standard Deviation and Variance

Reef Fish wrote:
DarkProtoman wrote:
What is the difference b/w the standard deviation and the variance
(other than the way they're calculated)? Like when are they used, or
when is one preferred over the other? Thanks!!!!

Good practical question!

Standard deviation is measured in the units in which the data is
measured.
That's why a confidence interval is in +- number of standard dev.
units.


Sorry for jumping in several days late--I've been on vacation. I fear that last statement could be confusing to intro stats students. A confidence interval is more typically described as point estimate +/- some number of *standard error* (SE) units. Of course, the SE *is* a standard deviation, but it is the SD of the sampling distribution of the statistic, not of the raw data.



It's more than just a preference. You can't calculate the standard
deviation
without calculating the variance first, by taking the square root of
it.

When is a variance prefered? Can't think of a good answer right off
hand.
It's used more for theoretical reasons than for practical usage. For
example,
the sample variance is an unbiased estimate of the variance, but nobody
I know ever uses an unbiased estimate of a standard deviation in
practice.

It's used in regression and other methods in breaking down the total
variation into component parts. I am sure others will name other
"prefered" uses of it.

-- Reef Fish Bob.



--
Bruce Weaver
bweaver@xxxxxxxxxxxx
www.angelfire.com/wv/bwhomedir
.

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