title: Shannon and Renyi entropies to classify effects of Mild Traumatic Brain Injury on postural sway.
abstract: BACKGROUND
  Mild Traumatic Brain Injury (mTBI) has been identified as a major public and military health concern both in the United States and worldwide. Characterizing the effects of mTBI on postural sway could be an important tool for assessing recovery from the injury.
  
  
  RESULTS
  We assess postural sway by motion of the center of pressure (COP). Methods for data reduction include calculation of area of COP and fractal analysis of COP motion time courses. We found that fractal scaling appears applicable to sway power above about 0.5 Hz, thus fractal characterization is only quantifying the secondary effects (a small fraction of total power) in the sway time series, and is not effective in quantifying long-term effects of mTBI on postural sway. We also found that the area of COP sensitively depends on the length of data series over which the COP is obtained. These weaknesses motivated us to use instead Shannon and Renyi entropies to assess postural instability following mTBI. These entropy measures have a number of appealing properties, including capacity for determination of the optimal length of the time series for analysis and a new interpretation of the area of COP.
  
  
  CONCLUSIONS
  Entropy analysis can readily detect postural instability in athletes at least 10 days post-concussion so that it appears promising as a sensitive measure of effects of mTBI on postural sway.
  
  
  BACKGROUND
  The programs for analyses may be obtained from the authors.
authors.affiliation: PMB Intelligence LLC, West Lafayette, Indiana, United States of America.
authors.forename: Jianbo
authors.initials: J
authors.lastname: Gao
authors.forename: Jing
authors.initials: J
authors.lastname: Hu
authors.forename: Thomas
authors.initials: T
authors.lastname: Buckley
authors.forename: Keith
authors.initials: K
authors.lastname: White
authors.forename: Chris
authors.initials: C
authors.lastname: Hass
mesh_terms: D000328:Adult; D056352:Athletes; D001924:Brain Concussion / Q000145:classification / Q000175:diagnosis; D001930:Brain Injuries / Q000145:classification / Q000175:diagnosis*; D019277:Entropy; D017709:Fractals; D006801:Humans; D015233:Models, Statistical; D004856:Postural Balance; D011187:Posture; D011312:Pressure; D011634:Public Health; D012720:Severity of Illness Index; D013997:Time Factors