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Dear Peter, many thanks,

I believe  that you are referring to BMS.DCM.rfx.bma.mEp  (without s) which gives me I think average estimates for the A matrix, B matrix or C matrix. 

So say I have 

1- group1.BMS.DCM.rfx.bma.mEp
2- group2.BMS.DCM.rfx.bma.mEp


I am kind of lost a bit of how I can compare them.. Do I have to perform a test but if so I should then have the subjects estimations, I think? or in other words how they can be compared ?

Many thanks

Adnan







On 5 November 2015 at 12:41, Zeidman, Peter <[log in to unmask]> wrote:

Dear Adnan,

If you’re comparing between groups, you don’t need the individual subjects’ estimates. Only the group average estimate from each group. It is fine if those averages is driven by a subset of subjects in each group.

 

Best,

P

 

From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of adnan alahmadi
Sent: 05 November 2015 11:00
To: [log in to unmask]
Subject: Re: [SPM] DCM BMA

 

Dear Peter,

 

Yes it does and make sense but the main question is that whether it is correct if I can compare say the A(1,3) connections among or between subjects although sometimes it is zeros in some subjects ?

 

Many thanks

 

Adnan

 

On 5 November 2015 at 10:55, Zeidman, Peter <[log in to unmask]> wrote:

Hi Adnan,

Presumably for subject 1 the only model(s) contributing to the average had connection A(1,3) enabled whereas for subject 2 the only model(s) contributing to the average had connection A(3,3) enabled. Does that fit with what you expect?

 

Best,

Peter

 

From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of adnan alahmadi
Sent: 04 November 2015 13:14
To: [log in to unmask]
Subject: [SPM] DCM BMA

 

Hi all.

 

What I understand the best approach to compare or investigate DCM is the use of BMA averaging. I have however couple of questions regarding this option.

 

Say for example I have two groups (or even one group). 

 

When I compare the models using compare, I should switch on the BMA option and then say choose family: winning family. 

 

Then the models are compared, no problem so far and I did this for both groups separately. 

 

So if I want to compare connections parameters between say two groups or within a group I should go to Group1.BMS.DCM.rfx.bma.mEps where I can find parameters of each subjects for all matrices. 

 

Say for example I look at the A matrix for subjects within a group or between groups. Sometimes I get missing values or zeros in some subjects and sometimes they are not. or in other words, 

 

Sometimes A matrix for subjects 1 is 

 

0 0 -0.4

0 0 0

0 0 0

 

While for subject 2 is 

0 0 0 

0 0 0

0 0 0.3

 

and so on. 

 

What is confusing is that why sometimes in the BMA there are zeros and this is dependent on subjects? 

 

When I tried to investigate the winning model and force DCM to do BMA of the winning model, I can see the values in the right place of connections, or in other words homogeneous among subjects.

 

 

Maybe it is my understanding but is it correct to compare A connection in the A matrix with zeros value in some subjects ? Or what is the right procedure to the comparison between groups when I want each group to preserve its winning model?

 

 

Many thanks

 

Adnan