# [Eeglablist] Time Frequency Statistics

Joseph Brooks jlbrooks at socrates.Berkeley.EDU
Fri Aug 27 16:20:04 PDT 2004

```David,

The time-frequency analysis is done using a function called timef. One of
the outputs of timef is a 2D matrix (time x frequency). This contains the
data that is used to generate the time-frequency map that you see.

In order to do a statistical analysis I do the following:

(1) Write a script that will run the timef function on data from each
subject and each condition.
(2) The script saves the outputs of each run of timef into a matlab
variable (I save things into structure variables....e.g. the structure may
contain fields for each condition and then the subjects within that).
(3) You can then save the output variables (a structure in my case) to disk.
(4) Now, the time-frequency maps can be accessed and you can select any
portion of the matrix that you choose.
(5) run your statistical analysis of choice on some sub-matrix of interest
of the time-frequency maps.
(6) to take the mean across subjects, just stack the matrices from all the
individual subjects into a 3D matrix and take the mean (using the mean
function in matlab) over the subject dimension.

Time and frequency are outputs of the timef function and will serve as axes
for the time-frequency matrix.

Type "help timef" at the matlab command line for full information about the
use of timef.

Let me know if I can clarify any of this.

Joe

At 02:48 PM 8/27/2004 +0000, you wrote:
>Hi
>Im doing some time frequency analysis, and have found positive results,
>but i need to run some kind of statistical analysis on them. How do I get
>to the data that produces the time frequency graph? Once I have that how
>do you define the parameters such as time and frequency?
>Many thanks
>
>David Schwartzman
>Oxford Brookes University
>
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```