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Re: st: obtain SD from P value for a paired t-test


From   Marcos Vinicius <bioestatistico@inbox.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: obtain SD from P value for a paired t-test
Date   Wed, 2 Oct 2013 04:20:10 -0800

Thank you Steve.
Regards,
Marcos
> -----Original Message-----
> From: sjsamuels@gmail.com
> Sent: Tue, 1 Oct 2013 18:37:59 -0400
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: obtain SD from P value for a paired t-test
> 
> 
> Marcos:
> 
> 
> You can't get the SD post without knowing the correlation of the pre &
> post measurements,
> since:
> 
> sd_diff = sqrt ( sd_pre^2 + sd_post^2  - 2 rho sd_pre sd_post)
> 
> Steve
> On Oct 1, 2013, at 1:56 PM, Marcos Vinicius wrote:
> 
> better formulating the question :obtaining the SD of the post measure
> using the   information bellow and additionally we know the N for the
> paired t test.
> 
> Vinicius
> -----Original Message-----
> From: bioestatistico@inbox.com
> Sent: Tue, 1 Oct 2013 09:48:14 -0800
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: obtain SD from P value for a paired t-test
> 
> Thanks Rich but not solved yet.
> I know the N,so I can get the standard deviation of the
> diference(post-pre).
> However I still don t know if it is possible to obtain the standard
> deviation corresponding to the post measure.
> Vinicius
>> -----Original Message-----
>> From: richgold@ix.netcom.com
>> Sent: Tue, 01 Oct 2013 13:04:47 -0400
>> To: statalist@hsphsun2.harvard.edu
>> Subject: Re: st: obtain SD from P value for a paired t-test
>> 
>> if you know N also, you can use the formula given in the Stata manual
>> (methods and formulas section of the ttest entry in the reference
>> manual), or many texts, to get the sd - if you don't know N, the best
>> you can do is an approximation
>> 
>> Rich
>> 
>> On 10/1/13 12:09 PM, Marcos Vinicius wrote:
>>> Hello,
>>> Anyone knows a way to obtain  standard deviation(sd) from P value for a
>>> paired t-test.?
>>> Consider that I know:
>>> Average pre
>>> SD pre
>>> Average post
>>> SD post (to be determined from others parameters)
>>> P value from paired t test
>>> 
>>> Average pre=6.5
>>> SD pre=1.8
>>> Average post =4.9
>>> SD post ??(to be determined from others parameters)
>>> P value from paired t test p=0.0003
>>> Any help would be greatly appreciated
>>> Thanks
>>> Vinicius
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