Thanks for the reply. 

Just to confirm, in this case then, the difference in means would be the con_image?

-Drew

From: <MCLAREN>, Donald <[log in to unmask]>
Reply-To: "MCLAREN, Donald" <[log in to unmask]>
Date: Monday, March 24, 2014 10:12 AM
To: "[log in to unmask]" <[log in to unmask]>
Subject: Re: [SPM] Paired t-test Effect Size

The effect size is the difference in means divided by the standard deviation.

The standard deviation is the the contrast (con_ image) divided by t-statistic (spmT_ image) times square root of N.  derived from t=M/(SD/square root of N)

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Sat, Mar 22, 2014 at 8:55 PM, Sevel,Landrew S <[log in to unmask]> wrote:

Hello all,

I'm interested in obtaining effect sizes to correspond to t-values for a repeated measures second level t-map. Is there a way to calculate an effect size from a group-level paired-samples t-test?

I know some approximations have been suggested for between-groups t-tests previously.

Thanks.

-Drew