Dear Axel,
The signal to noise ratio (SNR) is
simply given by the square of the
t-statistic, because
t = change in signal / noise standard
deviation
Hence, look at your t-maps and square
each value.
To get subject/group-specific SNRs
you'll need to make subject/group
-specific contrasts and then look at the
resulting t-maps.
Hope this helps.
Best wishes,
Will.
John Ashburner wrote:
> Dear Axel,
> I have passed your email on the the other members of the SPM development
> team who do a bit more of the time series analysis. My own stuff is
> mostly just spacial. Genarally, you can get an estimation of the signal
> from the beta or con images, whereas the estimated noise is stored in the
> ress image. I don't know about how this is all scaled though.
>
> All the best,
> -John
>
> On Sunday 08 December 2002 14:42, you wrote:
>
>>Dear John,
>>
>>I have a question concerning the signal to noise ratio.
>>We are planning a new experiment with old and young
>>subjects to figure out the magnitude of activation in a
>>specific region. In the case of a significant difference
>>between both groups we would like to calculateor to
>>determine the signal to noise ratio. To do this I think we
>>need the signal variance and the noise variance of our two groups.
>>But how can I get this values for each single subject of the old and
>>young group using SPM99?
>>
>
--
William D. Penny
Wellcome Department of Imaging Neuroscience
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7478
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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