title: Most suitable mother wavelet for the analysis of fractal properties of stride interval time series via the average wavelet coefficient method.
abstract: Human gait is a complex interaction of many nonlinear systems and stride intervals exhibiting self-similarity over long time scales that can be modeled as a fractal process. The scaling exponent represents the fractal degree and can be interpreted as a "biomarker" of relative diseases. The previous study showed that the average wavelet method provides the most accurate results to estimate this scaling exponent when applied to stride interval time series. The purpose of this paper is to determine the most suitable mother wavelet for the average wavelet method. This paper presents a comparative numerical analysis of 16 mother wavelets using simulated and real fractal signals. Simulated fractal signals were generated under varying signal lengths and scaling exponents that indicate a range of physiologically conceivable fractal signals. The five candidates were chosen due to their good performance on the mean square error test for both short and long signals. Next, we comparatively analyzed these five mother wavelets for physiologically relevant stride time series lengths. Our analysis showed that the symlet 2 mother wavelet provides a low mean square error and low variance for long time intervals and relatively low errors for short signal lengths. It can be considered as the most suitable mother function without the burden of considering the signal length.
authors.affiliation: Department of Electrical and Computer Engineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA.
authors.forename: Zhenwei
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Physical Therapy, University of Pittsburgh, Pittsburgh, PA 15260, USA.
authors.forename: Jessie
authors.initials: J
authors.lastname: VanSwearingen
authors.affiliation: Department of Physical Therapy, University of Pittsburgh, Pittsburgh, PA 15260, USA.
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Brach
authors.affiliation: Department of Medicine, Division of Geriatrics, University of Pittsburgh, Pittsburgh, PA 15261, USA.
authors.forename: Subashan
authors.initials: S
authors.lastname: Perera
authors.affiliation: Department of Electrical and Computer Engineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA. Electronic address: esejdic@ieee.org.
authors.forename: Ervin
authors.initials: E
authors.lastname: Sejdić
mesh_terms: D000465:Algorithms; D055592:Biophysical Phenomena; D017709:Fractals; D005684:Gait / Q000502:physiology*; D020233:Gait Disorders, Neurologic / Q000503:physiopathology; D006801:Humans; D012815:Signal Processing, Computer-Assisted
keywords: 1/f process; Fractals; Gait; Mother wavelet; Self-similarity; Stride intervals; Time series analysis; Wavelets