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From |
Michael McCulloch <mm@pinestreetfoundation.org> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: standard deviation for the difference in means |

Date |
Sun, 6 Jun 2010 18:07:42 -0700 |

On Jun 6, 2010, at 1:17 PM, Lachenbruch, Peter wrote:

Are you asking for pooled variance: sp^2=[(n1-1)s1^2+(n2-1)s2^2]/[n1+n2-2] ?Then the sd for the difference in the means will be sp*sqrt(1/n1+1/n2) aka standard error.________________________________________From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of Michael McCulloch [mm@pinestreetfoundation.org]Sent: Sunday, June 06, 2010 12:57 PM To: Statalist Statalist Subject: st: standard deviation for the difference in means 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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: RE: standard deviation for the difference in means***From:*"Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu>

**Re: st: RE: standard deviation for the difference in means***From:*Richard Goldstein <richgold@ix.netcom.com>

**Re: st: RE: standard deviation for the difference in means***From:*Michael Mitchell <Michael.Norman.Mitchell@gmail.com>

**References**:**st: standard deviation for the difference in means***From:*Michael McCulloch <mm@pinestreetfoundation.org>

**st: RE: standard deviation for the difference in means***From:*"Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu>

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