Hello,
please find my responses below.
Best regards,
Kersten
On Do, 2018-03-29 at 00:11 +0200, Kaushal, Mayank wrote:
Hi Kersten,
Apologies for the delay. I am still in the process of trying to figure out the
gaps in my understanding and would appreciate your inputs.
I created the design X from M using: X = [ones(length(M),1) M M(:,1).*M(:,3)
M(:,1).*M(:,4)];
The columns in X are as follows:
Column 1: intercept
Column 2: time_base_scan (This signifies the time elapsed from the base scan in
days. Each subject had upto 4 visits with scans
undertaken on each visit. For the scan taken on the first
visit 0 was entered in the qdec.dat.table file)
Column 3: age1stscan (This is the age of the subject at first scan)
Column 4: group 1 (Value of 1 entered in this column if the subject belonged to
group 1 and value of 0 entered in column 5 that signifies group 2)
Column 5: group 2 (Value of 1 entered in this column if the subject belonged to
group 2 and value of 0 entered in column 4 that signifies group 1)
Column 6: Column 2 (time_base_scan) x Column 4 (group 1)
Column 7: Column 2 (time_base_scan) x Column 4 (group 2)
So my understanding is that subjects belonging to group 3 have 0 in both
columns 4 and 5 and consequently, columns 6 and 7 would also be 0 for them.
This would be translated by matlab lme toolbox while doing spatiotemporal
analysis. Is my understanding correct?
Yes, this is correct, apart probably from a little typo:
Column 7 should read: " Column 2 (time_base_scan) x Column 5 (group 2)"
(group2 is column 5, not 4, in X; please adapt your design matrix if necessary)
Group 3 will be your reference group then, and will implicitly modeled by this
design matrix. I speculate this is what you mean by 'translated'.
I have attached X as well as M as separate excel files for your consideration.
In addition, I have attached qdec.dat.table file as well a word doc labeled
“workflow” that detail the order of matlab functions I have used to perform the
analysis.
My objective is to highlight clusters that are significantly different between
the groups over time using spatiotemporal analysis.
The contrasts used by me for the analysis: CM.C = [0 0 0 0 0 1 0; 0 0 0 0 0 -1
1]
Kindly comment on my choice of contrasts. Is this the correct choice for
contrasts if I want to find significant clusters based on cortical thickness
between all three groups over time?
Yes, the contrast is also correct for your purpose. It will identify regions in
which cortical thickness changes across time differ between groups.
Mayank
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