Which power metric to use to study the resting state data?
Published:
Relative power vs Absolute power vs Periodic power
EEG measures the electrical activity at a sensor relative to the reference & ground electrode. This causes issues in comparing absolute power between conditions &/participants as impedance differences can cause broadband shift in power. Relative power is often used as a substitute of absolute power as it supposedly normalizes w.r.t. the total power in the window of interest. However, using relative power to compare different conditions can cause spurious differences due to the nature of computation and this code is used to simulate a set of PSDs to evaluate when they fail and show how flattened PSD is a better alternative to quantify changes in multiple bands. 
In general, relative power is better when reporting which band has the highest power difference. Comparing multiple bands can lead to spurious differences due to the nature of computation. Periodic power is a much more robust alternative to quantify multi-band differences.
If power increase in two bands equally, their relationship in relative power is preserved in these bands but the power in other bands gets reduced even though in the original signal they are the same. Periodic power captures these differences well. Using absolute power on the other hand can cause artificial differences even due to simple broadband power differences which can also be due to non-physiological origins such as impedance differences. Either relative power or parameterized PSD helps with it.
If the power increase is small and limited to only one band, the differences are not distorted by neither relative power nor periodic power
However, the same band power if increased more, after a point it starts distorting the rest of the PSD and the relationship will be altered. As can be seen, the rest of the band power gets artificially increased and can lead to spurious reporting.
When multiple bands increase but one (theta) is much bigger than the other (alpha), not even the increase in alpha power will be represented correctly (the relationship is flipped).
**An important point to keep in mind is that ASR is based on Principal component analysis. A concern is there is 4 ch only and so 4 PCs. The reconstruction will be lossy and not ideal. Thread is not intended to say the method is error-proof, but an option to consider & to emphasize not to go with default:)