[FieldTrip] impact of skewed power distributions on data analysis

[Giuseppe Pellizzer]

You are definitely correct, the distribution of power is highly skewed.
However, using the log-transform does a pretty decent job at 'normalizing'
the distribution.
A related issue is that when comparing power during a task with baseline,
the ratio Task Power/Baseline Power is highly asymmetric (because it is
equal to 1 when Task Power=Baseline Power, and it can only go down to 0 on
one side and can go to infinity on the other). For all of those reasons, it
is better to use the log-transform of the ratio of power, that is, log(Task
Power/Baseline Power)=log(Task Power) - Log(Baseline Power) (when using
Log10 the result can be expressed in dB by multiplying it by 10).

Giuseppe Pellizzer
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