The problem described below persists (I have no also reproduced the same
error on every computer I could get my hands on), however, I have managed to
narrow the potential source of the problem down a bit:
The 2-sample t-test aims to compare group 1 (10 first level .con images)
with group 2 (10 first level .con images).
When I run this second level 2-sample t-test it produces valid looking beta
images for both groups (beta1 for group1 and beta2 for group2). The produced
con image also looks good and corresponds to the difference between beta1
and beta2. The resMS image also looks believable. However, the spmT image
produced from the comparison of the con image to the resMS image contains
only the value 0, which should not be possible.
Hopefully this additional information will allow someone to find out what
goes wrong here.... Unfortunately it is very important that I get this
2-sample t-test to work again on spm2.
Many thanks in advance,
Bianca de Haan
On Thu, 17 Jan 2008 18:29:33 +0000, B. de Haan
<[log in to unmask]> wrote:
>Dear SPM-list,
>
>I am having some problems when trying to reanalyze old data with spm2:
>
>two-sample t-tests between two groups suddenly seem to produce only empty
>spmT images (the whole spmT_000x image is 0). I've been using spm2 for years
>and have never encountered this problem.
>
>
>1) This problem is specific to two-sample t-tests between the 2 groups;
>one-sample t-tests in spm2 on each of the 2 groups work fine and produce the
>same results they did a year ago.
>
>2) This problem is also specific to spm2; the same two-sample t-test between
>the 2 groups using spm5 works fine and produces the same results as I got a
>year ago with spm2.
>
>3) 2-group ANOVA in spm2 (should produce the same results as 2-sample
>t-test) again only produces empty spmT images.
>
>4) I have re-downloaded and installed spm2 and tried the two-sample t-test
>on both Matlab6.5 and Matlab7.1. All to no avail.
>
>5) The 2-sample t-test design matrix from the current analysis looks
>radically different from the design matrix from the analysis I performed a
>year ago and I do not seem to be able to reproduce the design matrix from a
>year ago in spm2 anymore (I tried every combination of the 2-sample t-test
>settings possible). However, as mentioned above, if I do the same 2-sample
>t-test in spm5, I obtain the same results as I did a year ago again,
>therefore I feel confident that my 'old' results are valid.
>
>
>I am pretty much at my wits end as to why I no longer can perform 2-sample
>t-tests in spm2. I would really like to stick with spm2 for this old dataset
>(am just trying to do a few small additional analyses in response to
>reviewer's comments). Does anybody have any idea what might be going on here
>and how to solve this?
>
>Many thanks in advance,
>
>Bianca de Haan
>========================================================================
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