Hi Donald，
Thanks for the nice and helpful suggestion. I think it is the point
that I missed in my data processing.
Thanks again.
Bests!
-------------------------------------------------------------------
Hongjian He
Zhejiang University, Hangzhou, China.
Email: hehongj(AT)gmail.com
On Mon, Jul 11, 2011 at 2:46 AM, MCLAREN, Donald
<[log in to unmask]> wrote:
> In SPM, there is also a high-pass filter that is applied to the data.
>
> If you look in spm_spm:
>
> W will be an identity matrix if you turn off AR(1)
> xX.K is the high-pass filter.
>
> xX.xKXs = spm_sp('Set',spm_filter(xX.K,W*xX.X)); % KWX
> xX.xKXs.X = full(xX.xKXs.X);
> xX.pKX = spm_sp('x-',xX.xKXs);
> KWY = spm_filter(xX.K,W*Y);
> beta = xX.pKX*KWY;
>
> Best Regards, Donald McLaren
> =================
> D.G. McLaren, Ph.D.
> Postdoctoral Research Fellow, GRECC, Bedford VA
> Research Fellow, Department of Neurology, Massachusetts General Hospital and
> Harvard Medical School
> Office: (773) 406-2464
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> On Sun, Jul 10, 2011 at 2:17 PM, Hongjian He <[log in to unmask]> wrote:
>> Dear all,
>> Does anyone have any idea about the beta calculation in SPM? I found
>> it different with what I got from matlab regression.
>> I run SPM with a simple first level model with the design matrix
>> including two task condition, a linear trend term and a dc-term. No
>> global normalization and AR(1) are specified. After the estimation, I
>> can find the beta value for a example voxel, such as 0.5288.
>>
>> I then take the time series of that voxel (Y), and do the regression
>> in matlab. The design matrix (or regressors X) has been set to be
>> exactly the same with SPM.xX.X. To find the beta value, I did the
>> calculation as (X' * X) \ X' * Y. However, the value I got is
>> -4.9671. I also considered the percentage unit, and did the
>> normalization with a factor of 100/dc-term. The result of that is
>> -0.6954.
>>
>> Could anyone help me to understand the procedure I missed to find the
>> same regression value for the two cases?
>>
>> Thanks in advance!
>> -------------------------------------------------------------------
>> Hongjian He
>> Zhejiang University, Hangzhou, China.
>> Email: hehongj(AT)gmail.com
>>
>
