Dear all

 

I am using the lme toolbox to perform a longitudinal comparison of cortical thickness among 4 patient groups. Following the lme tutorial, I concatenated all files and I built a design matrix with following columns:

 

-one column for intercept (all ones)

-one column for time

-four columns for each group (1 for subjects belonging to the group, zero otherwise)

-four columns for group by time interaction

 

I then built appropriate contrasts to test the effects of time, group and time x group effect; e.g., to test time x group interaction between group 1 and group 2, I built the following contrast:

 

CM.C=[0 0 0 0 0 0 1 -1 0 0]

 

However, I obtain quite strange results, because I get a lot of very small, very significant clusters of difference (having max t value = inf or –inf).

Do you have any idea of the reason why I am getting this strange output? In your opinion, is there anything wrong in my design matrix or in the way I defined the contrasts?

This is the first time I am trying to compare four groups in the same LME models, I previously ran LME statistics including just one or two groups, and everything ran smoothly.

 

Please see a snapshot of my output statistic below:

 

# ClusterNo  Max   VtxMax   Size(mm^2)  TalX   TalY   TalZ    NVtxs   Annot
   1         -inf  112586      0.96    -19.0  -95.2    8.3     1  lateraloccipital
   2         -inf   93693      0.89    -22.0   54.4   16.4     1  rostralmiddlefrontal
   3          inf   29207      0.86    -35.9   46.6   -9.9     1  parsorbitalis
   4          inf  158564      0.78    -13.7  -98.8    2.3     1  lateraloccipital
   5         -inf   67614      0.69     -8.3   35.1   25.4     1  superiorfrontal
   6         -inf  123144      0.69    -40.3   19.5   29.8     1  caudalmiddlefrontal
   7         -inf    2273      0.68    -55.6  -30.9   24.2     1  supramarginal
   8         -inf  140663      0.67     -6.2   39.1   -4.4     1  rostralanteriorcingulate
   9         -inf    5857      0.64    -35.5    8.6   50.8     1  caudalmiddlefrontal
  10          inf   87756      0.61    -14.1  -98.2    1.7     1  lateraloccipital
  11          inf   95576      0.56    -43.9   24.5   27.5     1  rostralmiddlefrontal
  12         -inf  112122      0.56    -29.0  -62.8   35.9     1  inferiorparietal
  13          inf   54800      0.54    -18.7  -59.3    2.6     1  lingual
  14         -inf  140378      0.53    -19.0  -42.5   62.6     1  superiorparietal
  15          inf   99044      0.49    -43.7  -20.0   52.6     1  postcentral
  16          inf  119372      0.47    -52.1   -2.5   25.5     1  precentral
  17         -inf  125951      0.47    -44.3  -55.1   12.7     1  inferiorparietal
  18          inf    8776      0.46    -57.0   -2.0   11.7     1  precentral
  19          inf   10137      0.44    -27.8  -49.8   -1.9     1  lingual
  20          inf   20153      0.42     -6.6   13.8   29.5     1  caudalanteriorcingulate
  21         -inf   19380      0.40    -61.6   -8.6   13.7     1  postcentral
  22         -inf   38802      0.39    -23.9  -56.1   49.0     1  superiorparietal
  23          inf   53936      0.38    -45.3  -25.9   46.7     1  postcentral
  24          inf   45406      0.35    -38.8  -36.8   36.7     1  supramarginal
  25         -inf   46213      0.32     -6.4  -47.6   15.7     1  isthmuscingulate
  26          inf   41829      0.26    -61.1   -8.7   10.5     1  postcentral
  27      -13.032   76609      0.40    -14.4  -15.8   64.7     1  precentral
  28       12.272   78924      0.27     -6.0   -6.5   30.3     1  posteriorcingulate
  29      -10.960     822      0.63    -51.8  -30.1  -17.2     1  inferiortemporal
  30       10.326   96572      0.48    -31.7   11.6    0.5     1  insula
  31       -8.509   43473      0.54    -62.2  -26.3    6.7     1  superiortemporal

.. continued with a lot of significant clusters, all 1 vertex in size ..

 

 

Thank you for any suggestion

Best regards

 

Paola