Dear Mobin,

 

DCM can handle any amount of signal to noise. To get an idea of how much noise can be tolerated for any particular question, one would do simulations with increasing levels of noise and simulate the model comparison of interest.  The noise level that renders the difference in free energy (DCM.F) less than 3 is the level of noise at which your data are too noisy to provide evidence for one model over another. I think Klaas wrote an SPM routine to generate simulated data, given a model specification (a DCM structure).

 

I hope this helps.

 

With very best wishes,

 

Karl