The "Vertex Analysis: requires you to prepare two files: the individual segmented structures combined into one file, and a design matrix to indicate which file belongs to which group.
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The files will be ordered alphabetically; knowing the order is required for the later steps (specifically, creating the design matrix).
Design matrix
The design matrix is common to FSL statistical routines, and is the same as created in SPM. However, for FIRST there are some differences (see "Create a design matrix" in guide). Specifically, the group should be in one rather than two columns, and F tests should be used.
Note: Create this file using the FSL "Glm" GUI, as other important files are created at the same time.
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The design matrix is a text file with header information and numbers in columns. By tradition, the file is saved with a name like "design.mat". Each row represents a subject, in the order stored in the concatenated bvars file. The simplest design matrix (for a two group dataset) is a two columns, with the first +1 for rows in group 1 and 0 otherwise, and similarly +1 in the second column for rows in the second group. There is also header information which includes the number of columns (I think), the number of subjects, and the maximum value of each column. For example, here is a two-group, 5 subjects/group design matrix:
Glm from FSL GUI
Type "fsl" to start the FSL GUI, click "Misc " then "GLM Setup".
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