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ANOVA
EEG and MEG
studies are most often analyzed with a special kind of analysis of
variance, that accounts also for within subject changes rather than
only for
between subject differences. EMEGS offers the possibility to calculate
this kind of analysis directly, without exporting the data to a
separate statistic software package. At the present time, only
single
region-of-interest analyses are supported. Pointwise analyses on all
sensors are under construction.
ANOVAs require the R environment for statistical computing to be setup
correctly, as described here.
1. Prepare data files and batch
To run a repeated measures ANOVA, prepare your data as follows: each
condition for every subject has to be saved as
an SCADS
average file. Every file has to have the same number of points and
number of channels. You need a
batch listing the paths of those files on your
machine.This batch must be setup using the batch docking window and has
to reflect the design of the planned
analysis, that is, your paths have to be listed according to the
hierarchy of the factors of your statistical design. The lowest
level is always the
subject
factor, so you 'll start with one cell for which all subjects average
files are given.
Beneath that, you list all subjects average files for the next cell
etc. The subject order has to be identical in every cell, and you have
to have equal number of subjects in every cell. Please note that the
structure of the batchfile is identical, wether or not you have
defined one or more between factor(s)!
Cells need to be ordered from lowest
hierarchy position of
the factor to highest hierarchy position. For instance, consider
a
2x2x2 design with the factors 'task'
(count forward vs count backward) , 'color' (count red squares
vs. count green squares) and 'gender'. Thus, your batch for 16 subjects
for this design has to have
the following form:
2. Set Interval and Sensor group
settings
Select from the Calculate menu
ANOVA::Run ANOVA, and on the value export page of the displayed dialog,
make sure that the displayed summary of the calculations is correct
(includes Baseline, Group and Intervals):
3. Enter the factorial design on the Calculate: ANOVA dialog
Then enter your statistical design and second page as shown below:
4. Set the design
Push the large set factorial design button
on the bottom right corner, to have EMEGS check the design
correspondance with the current batch. If inconsistencies are
found, you will get an error message, otherwise, the Ok button is enabled, which you push
to start the ANOVA.
5. Check Export- and ANOVA-log
During the value export, EMEGS writes messages to the log docking
window. If the log window is not visible