table of contents
LIPSIA     Two-sample t-test in ROIs
vROItwosample_ttest
This program performs a two-sample 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 two-sample t-test between these two lists against the null hypothesis of "no difference" between the groups. Example:

vROItwosample_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     addr   mm^3   t z p
1     0.11     0.41     44.50     70     -2.176     -1.941     0.0261
2     0.08     0.44     30.50     494     -1.031     -0.985     0.1623
3     -0.05     0.26     30.50     494     -0.629     -0.609     0.2712
4     0.22     0.66     27.00     76     -0.578     -0.561     0.2874
5     0.67     1.04     13.00     61     0.553     0.537     0.2957

In this example, five ROIs were present. Only the first ROI shows a significant effect (p < 0.05). The ROI-size is given in mm^3. The address refers to the center of gravity of the ROI. It is given in Talairach coordinates.

Parameters of 'vROItwosample_ttest':
-help
Prints usage information.
-in1
Input files of group 1. Default: (none)
-in2
Input files of group 2. Default: (none)
-mask
File 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.