Factors affecting the reliability of transfer function estimates ofcardiovascular variability signals

摘要

The reliability of transfer function (TF) estimates has beentraditionally judged according to the threshold value of 0.5 in themagnitude squared coherence (MSC). However, other parameters affect thereliability as well, and low MSC values are often unavoidable inphysiological systems. The study was devised (1) to assess by computersimulations the applicability of theoretical expressions for the errorof TF estimates, (2) to provide error curves for TF estimates as afunction of major experimental and analysis parameters and (3) toevaluate the fidelity of observed TF shapes with respect to expectedones when the MSC is low. Theoretical confidence intervals for the TFmagnitude were found to be accurate enough to be used in practicalanalysis. Curves for the normalized bias and SD of TF estimates werederived, providing useful information for appropriate design of datacollection and analysis. With an appropriate choice of analysisparameters the shape of observed TFs were found to be close to theexpected ones even when the MSC is <0.5