table of contents
LIPSIA     Paired t-test in ROIs
vROIpaired_ttest
This program performs a paired t-test on regions of interest (ROIs) across two groups of contrast images. The ROIs are specified in a mask file. It can be constructed either interactively using the progam 'vledit', or offline using 'vmaskedit'.

For each ROI within the mask, the program first computes the average across the contrast values within each data set separately. It thus obtains two lists of averaged contrast values, where the number of elements in each list corresponds to the number of contrast images in the two gropus.

It then performs a paired t-test between these two lists against the null hypothesis of "no difference" between the groups. Example:

vROIpaired_ttest -in1 cgroup1_*.v -in2 cgroup2_*.v mask mask.v -report liste.txt

This call prints the statistical analysis to the terminal and to an ASCII-file. A typical output may for instance look like this:

  ROI   mean   t z p
1     0.4 (0.03)     -2.176     -1.941     0.0261
2     0.5 (0.01)     -1.031     -0.985     0.1623
3     -0.1 (0.02)     -0.629     -0.609     0.2712
4     -0.2 (0.05)     -0.578     -0.561     0.2874
5     0.3 (0.02)     0.553     0.537     0.2957

The column headed "mean" gives the pairwise difference averaged across all contrast images. The number in brackets denotes the standard error.

It is possible to use a different mask for each pair of contrast images. In this case, the number of pairs and masks much match, and the number of ROIs and their IDs should be consistent across all masks. An '*' can be used to specify multiple input files. The files are then processed in lexicographical order. Please make sure that the lexicographical order of filenames is consistent so that each pair of contrast images is matched to the correct mask.

vROIpaired_ttest -in1 cgroup1_*.v -in2 cgroup2_*.v -mask mask_*.v -report liste.txt

Parameters of 'vROIpaired_ttest':
-help
Prints usage information.
-in1
Input files of group 1. Default: (none)
-in2
Input files of group 2. Default: (none)
-mask
File(s) containing ROIs. Default: (none)
-report
ASCII-File containing output report. Default: (none)


Literature:
Bosch, V. (2000). "Statistical Analysis of Multi-Subject fMRI Data: Assessment of Focal Activations." Journal of Magnetic Resonance Imaging, 11(1), 61-64.
Max Planck Institute for Human Cognitive and Brain Sciences. Further Information: lipsia@cbs.mpg.de
Copyright © 2007 Max Planck Institute for Human Cognitive and Brain Sciences. All rights reserved.