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FMRI Group Analysis: Examples
GLM
Design matrix
Effect size subject-series
Voxel-wise group analysis
Groupeffect sizestatistics
Subjectgroupings
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Standard-spacebrain atlas
subjects
Single-subject effect sizestatistics
Single-subject effect sizestatistics
Single-subject effect sizestatistics
Single-subject effect sizestatistics
subjects
Registersubjects intoa standardspace
Effect sizestatistics
Statistic ImageSignificant
voxels/clusters
Contrast
Thresholding
Examples
Single Group Average
• We have 8 subjects - all in one group - and want the mean group average:
Does the group activate on average?
• estimate mean
• estimate std-error(FE or ME)
• test significance of mean > 0
>0?
0
subj
ect
effect size
Single Group Average
Does the group activate on average?
0
subj
ect
effect size
Single Group Average
Does the group activate on average?
Unpaired Two-Group Difference• We have two groups (e.g. 9 patients, 7 controls)
with different between-subject variance
Is there a significant group difference?
• estimate means
• estimate std-errors(FE or ME)
• test significance of difference in means
>0?0
subj
ect
effect size
Unpaired Two-Group Difference
Is there a significant group difference?
0
subj
ect
effect size
Unpaired Two-Group Difference
Is there a significant group difference?
0
subj
ect
effect size
Unpaired Two-Group Difference
Is there a significant group difference?
Paired T-Test• 8 subjects scanned under 2 conditions (A,B)
Is there a significant difference between conditions?
0
subj
ect
effect size
>0?
Paired T-Test• 8 subjects scanned under 2 conditions (A,B)
Is there a significant difference between conditions?
0
subj
ect
effect size
try non-paired t-test
• 8 subjects scanned under 2 conditions (A,B)
Is there a significant difference between conditions?
de-meaned data
0su
bjec
teffect size
data
0
subj
ect
effect size
Paired T-Test
subject mean accounts for large prop.of the overall variance
• 8 subjects scanned under 2 conditions (A,B)
Is there a significant difference between conditions?
de-meaned data
0su
bjec
teffect size
data
0
subj
ect
effect size
Paired T-Test
>0?subject mean
accounts for large prop.of the overall variance
subj
ect
effect size00
Paired T-Test
Is there a significant difference between conditions?
subj
ect
effect size00
Paired T-Test
Is there a significant difference between conditions?
Paired T-Test
Is there a significant difference between conditions?
EV1models the A-B paired difference; EVs
2-9 are confounds which model out each
subject’s mean
Paired T-Test
Is there a significant difference between conditions?