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?