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[wiki:FsTutorial top] | [wiki:FsTutorial/GroupAnalysis previous]

• To follow this exercise exactly be sure you've downloaded the [wiki:FsTutorial/Data tutorial data set] before you begin. If you choose not to download the data set you can follow these instructions on your own data, but you will have to substitute your own specific paths and subject names.

## Specify contrast vectors to test hypotheses

The design matrix generated from the FSGD file consists of the last three columns of:

```SubjectID  Male  Female  Age

004      1      0     22
008      0      1     88
017      1      0     25
021      1      0     22
032      1      0     79
039      0      1     69
040      0      1     24
045      0      1     78
049      1      0     19
067      1      0     71
073      1      0     77
074      1      0     85
080      1      0     23
084      1      0     21
091      0      1     23
092      1      0     29
093      0      1     22
095      0      1     70
097      1      0     74
099      0      1     93
102      0      1     82
103      0      1     66
106      1      0     27
108      1      0     28
111      0      1     81
114      0      1     87
123      0      1     69
124      0      1     30
128      1      0     90
129      0      1     65
130      1      0     68
131      0      1     80
133      0      1     73
136      0      1     78
138      0      1     26
140      0      1     18
141      0      1     20
144      1      0     78
145      1      0     80
149      1      0     77```

There are three regressors. The first regressor codes membership in the Male group. The second codes for membership in the Female group. The last is the age for the subject. The contrast vector for testing the given subjects for straight correlation between thickness and age can be specified as:

`[0 0 1]`

The contrast vector has three components because there are three regressors.

To use this in your mri_glmfit command create a file that contains just the one line of your contrast vector using the text editor of your choice. Again, using an appropriate naming convention is a good idea. Make sure this contrast vector has been created for you and is called age.mat:

```cd \$FREESURFER_HOME/subjects/buckner_data/tutorial_subjs/group_analysis_tutorial/stats
cat age.mat```

Create age.mat if it does not exist. It should contain this line:

`[0 0 1]`

As an additional exercise, try constructing the contrast vector for testing the same data for difference between males and females independent of age. [wiki:FsTutorial/MaleFemaleContrastSolution Click here for the answer.]

FsTutorial/CreateContrastVectors (last edited 2008-04-29 11:46:15 by localhost)