Miguel,

1- the 'average' referred to in the display question refers to each vertex on the group average surface, and is the mean of all subjects in a group. Ctrl-right click on a vertex to bring up a data plot to see this raw data. the actual display is the p-value (-log10) of the contrast avgA-avgB. negative values means its thinning.

2- the import button just does the work for you. you used to have to do it manually.

3- it using lh_parahippocampal thickness as a covariate (along with groups A and B in your example), so its looking a thickness changes everywhere in relation to lh_parahip thickness. imagine if you had selected hippocampal volume: a reduced size hippocampus would show its effects across a lot of areas of cortex. a positive value means it thickening in those areas.

Nick

On Mon, 2009-06-22 at 07:47 -0700, Jose Soares wrote:

Hi all,

I am a little bit confused about the qdec display. I have some simple questions about two groups A and B:

1- In the question, does the average thickness differ between A and B? How this average is calculated? By the difference between the A average and B average (avgA-avgB) ? The negative values (normally in blue) mean that the thickness (average of B) B is higher than A?

2- I want to analyze lh parahippocampal thickness. What is the difference between insert the values manually in the qdec.table.dat file (like the tutorial) or import ( in subjects - stats data import) the lh_parahippocampal_thickness from aparc?

3- In the question, does the thickness--lh_parahippocampal_thickness correlation differ between A and B? what for instance a positive value mean on display? I only expected results in the parahippocampal area...

Thaks for the help,

Miguel.

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