For only one group you don't need a group variable. you'd drop beta 3 and 4
terms.
Yolanda Vives <yvi...@pic.es> wrote:
>Thank you Martin!
>
>For only one group, would the design matrix be the same but
>intercept=Group=all ones?
>
>Yij = ß1 + ß2*tij +ß3*Group + ß4*Group *tij + ß5*Genderi + ß6*Agei +
>ß7*ICVi+ b
>1i + b2i*tij + eij
>
>Regards,
>Yolanda
>
>2013/5/28 Martin Reuter <mreu...@nmr.mgh.harvard.edu>
>
>> Hi Yolanda,
>>
>> since you have the intercept you don't need both group1 and group2
>(as one
>> is 1 - the other), so drop beta 5 and 6 terms.
>> If you want to test if the slope is different between the groups
>differ
>> just look at beta4 which is checking if slope1-slope2 different from
>zero.
>> If it is negative slope2 is larger, if positive slope1 is larger.
>Note that
>> if your slopes are negative, e.g. atrophy, then larger means closer
>to zero
>> = less atrophy.
>>
>> Best, Martin
>>
>>
>> On 05/28/2013 11:57 AM, Yolanda Vives wrote:
>>
>> Dear FreeSurfer experts,
>>
>> I am trying to use the LME toolbox to analyse the hippocampal change
>over
>> time in a group and also among 2 groups (2 scans per subject).
>>
>> When I estimate the parameters with lme_fit_FS I become a warning
>saying
>> that the matrix is singular and my results are NaN. I guess that my
>design
>> matrix X is not correct, can you please help me?
>>
>> I have followed the example from the wiki. My model for the two
>groups
>> study is the following:
>>
>> Yij = ß1 + ß2*tij +ß3*Group1 + ß4*Group1 *tij + ß5*Group2 + ß6*Group2
>*tij+ ß
>> 7*Genderi + ß8*Agei + ß9*ICVi + b1i + b2i*tij + eij
>>
>> 1) intercept (all ones)
>>
>> 2) time (tij) . Here I have 0s for the first scan of each subject and
>a
>> number in years for the second scans. Is it correct?
>>
>> 3) one for Group1 and zero otherwise
>>
>> 4) colum 3) .* time
>>
>> 5) one for Group2 and zero otherwise
>>
>> 6) colum 5) .* time
>>
>> 7) Gender
>>
>> 8) Age of the subject at each scan moment.
>>
>> 9) ICV (converted to liters).
>>
>> Thank you in advance,
>> Yolanda
>>
>>
>> _______________________________________________
>> Freesurfer mailing
>listfreesur...@nmr.mgh.harvard.eduhttps://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
>>
>>
>> --
>> Martin Reuter, Ph.D.
>> Assistant in Neuroscience - Massachusetts General Hospital
>> Instructor in Neurology - Harvard Medical School
>> MGH / HMS / MIT
>>
>> A.A.Martinos Center for Biomedical Imaging
>> 149 Thirteenth Street, Suite 2301
>> Charlestown, MA 02129
>>
>> Phone: +1-617-724-5652
>> Email:
>> mreu...@nmr.mgh.harvard.edu
>> reu...@mit.edu
>> Web : http://reuter.mit.edu
>>
>> The information in this e-mail is intended only for the person to
>whom
>> it is
>> addressed. If you believe this e-mail was sent to you in error and
>the
>> e-mail
>> contains patient information, please contact the Partners Compliance
>> HelpLine at
>> http://www.partners.org/complianceline . If the e-mail was sent to
>you in
>> error
>> but does not contain patient information, please contact the sender
>and
>> properly
>> dispose of the e-mail.
>>
--
Sent from my phone. Please excuse my brevity.
_______________________________________________
Freesurfer mailing list
Freesurfer@nmr.mgh.harvard.edu
https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
The information in this e-mail is intended only for the person to whom it is
addressed. If you believe this e-mail was sent to you in error and the e-mail
contains patient information, please contact the Partners Compliance HelpLine at
http://www.partners.org/complianceline . If the e-mail was sent to you in error
but does not contain patient information, please contact the sender and properly
dispose of the e-mail.
