Congi, M., G. Calcagnini, S. Lino, S. Cerutti, and S. Damiani. “A Statistical Comparison of Signal Representations and Spectral Estimators of Heart Rate Variability in Hypertensive Patients”. Statistica, vol. 62, no. 1, Jan. 2002, pp. 167-74, doi:10.6092/issn.1973-2201/399.