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st: standard deviation for the difference in means


From   Michael McCulloch <mm@pinestreetfoundation.org>
To   Statalist Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: standard deviation for the difference in means
Date   Sun, 6 Jun 2010 12:57:51 -0700

Apologies for a basic statistics question:

I wish to estimate sample size for an experiment in which, from previously published data, I have available the following summary measures (but not the raw data):

Group A:
	mean of a continuous variable
	standard deviation of that continuous variable
	sample size
Group B:
	mean of the same continuous variable
	standard deviation of that continuous variable
	sample size
And, the P value based on two-sample t tests comparing differences in between-group means.


My question is, with those values (and none other) available, is it possible to estimate the standard deviation for the difference in between-group means.


Best wishes,

Michael McCulloch, LAc MPH PhD
Pine Street Foundation
124 Pine Street
San Anselmo, CA 94960-2674
tel:	415-407-1357
fax: 	206-338-2391

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