Kewei Chen wrote:
>
> See if my statements below are right, Will:
>
> though the test of rp>0 is equivalent to the test of the corresponding
> regression coefficient (beta)>0, the test of rp_1 > rp_2' is not
> equivalent to the test of 'beta_1 > beta_2'
>
Off the top of my head I would have said that it is equivalent.
Will.
> Kewei
>
>
> On Wed, 2 Feb 2005, Will Penny wrote:
>
>> Dear Denise,
>>
>> If your GLM analysis used a design matrix with a single regressor,
>> there is a 1 to 1 relationship between the correlation
>> coefficient, r, (of regressor and data) and regression coefficient, beta,
>> which is
>>
>> r = beta * s_x/s_y
>>
>> where s_x is the standard deviation (SD) of the regressor and
>> s_y is the SD of the data.
>>
>> If beta is inferred to be significantly non-zero, using eg. a t/F-test,
>> then r is guaranteed to be significantly non-zero.
>>
>> If your GLM analysis contains a design matrix with multiple
>> regressors, as is usually the case, then there exists a one
>> to one relationship between each regression coefficient
>> and its corresponding *partial* correlation coefficient, rp, ie.
>> the correlation between that regressor and the data after having
>> subtracted from the data what can be explained by the other regressors.
>>
>> Again, if the regression coefficient is inferred to be significantly
>> non-zero then rp will also be.
>>
>> But there's no easy way of getting the r/rp values out of SPM2.
>> You'll have to matlab it.
>>
>> Best,
>>
>> Will.
>>
>> Denise Dörfel wrote:
>>
>>> Hi SPM users,
>>>
>>> I did a correlation analysis between the activation of a contrast and
>>> the score of a questionnaire.
>>> Is it possible to show the correlation coefficient or to get it out
>>> of SPM2?
>>>
>>> In general, how can I get infos like this out of SPM2?
>>>
>>> Thanks in advance.
>>> Denise Dörfel.
>>>
>>
>> --
>> William D. Penny
>> Wellcome Department of Imaging Neuroscience
>> University College London
>> 12 Queen Square
>> London WC1N 3BG
>>
>> Tel: 020 7833 7475
>> FAX: 020 7813 1420
>> Email: [log in to unmask]
>> URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
>>
--
William D. Penny
Wellcome Department of Imaging Neuroscience
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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