EEG and Brain Connectivity: A Tutorial - Bio-Medical Instruments, Inc.

Coherence inflation is defined as any value of coherence (x) greater
than zero when coherence (or correlation) is computed using pure Gaussian
noise in one of the two channels and a pure sine wave in the other channel.
Eq. 20- Coherence Inflation x > 0
This is the error term when one of the channels is pure Gaussian noise and
the second channel is signal. Any value of coherence > 0 is due to error
attributable to low degrees of freedom, inadequate signal resolution or too
short of measurement interval, or improper sample rates within that interval,
etc.
Figure 18 below shows an example of a 5 Hz 10uVsine wave in one
channel and 100 uV (p-p) gaussian noise in the second channel. The power
spectrum of the two channels is shown in the upper right panel. Figure 18 is
just one example of the analyses performed by the NeuroGuide Signal
Generator that directly test EEG simulated EEG cross-spectra.
Figure 18. Screen capture of the NeuroGuide signal generation program.