Anna:
I have done this before trying to get an estimate of effect size
[(mean1-mean2) / s], and the standard deviations for the groups differed. I did
it by getting the pooled variance first (formulas in most stat books) and
squared rooted it. But this was for only two groups, and all I needed was a
quick estimate for power and sample size estimation.
You wouldn't want to pool if you had reason to believe the variances within
the groups differed (as in Levene'e test for homogeneity of variance). If all
you want is a quick estimate, I think you can simply take the MS(within) from
an omnibus anova, and take the square root of it.
Just curious: What are you planning to do with a pooled standard deviation?
Anna Geyer wrote:
> How do I calculate pooled standard deviation? I have
> study with group of exercisers following forward over
> time. I want look at weight by category of calorie
> intake. I look at standard deviation for weight for
> each calorie group but want one overall standard
> deviation. Is this valid? Thank you
> __________________________________________________
> Do You Yahoo!?
> Talk to your friends online with Yahoo! Messenger.
> http://im.yahoo.com
>
> ===========================================================================
> This list is open to everyone. Occasionally, people lacking respect
> for other members of the list send messages that are inappropriate
> or unrelated to the list's discussion topics. Please just delete the
> offensive email.
>
> For information concerning the list, please see the following web page:
> http://jse.stat.ncsu.edu/
> ===========================================================================
--
---------------------------------------------------------------
John W. Kulig [EMAIL PROTECTED]
Department of Psychology http://oz.plymouth.edu
Plymouth State College tel: (603) 535-2468
Plymouth NH USA 03264 fax: (603) 535-2412
---------------------------------------------------------------
"The only rational way of educating is to be an example - if
one can't help it, a warning example." A. Einstein, 1934.
===========================================================================
This list is open to everyone. Occasionally, people lacking respect
for other members of the list send messages that are inappropriate
or unrelated to the list's discussion topics. Please just delete the
offensive email.
For information concerning the list, please see the following web page:
http://jse.stat.ncsu.edu/
===========================================================================
