Postural stability index is a more valid measure of stability than equilibrium score

Hans Chaudhry, Thomas Findley, Karen S. Quigley, Zhiming Ji, Miriam Maney, Tiffany Sims, Bruce Bukiet, Richard Foulds

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


Researchers, therapists, and physicians often use equilibrium score (ES) from the Sensory Organization Test, a key test in the NeuroCom EquiTest System (a dynamic posturography system) to assess stability. ES reflects the overall coordination of the visual, proprioceptive, and vestibular systems for maintaining standing posture. In our earlier article, we proposed a new measure of anterior-posterior (A-P) postural stability called the Postural Stability Index (PSI), which accounts for more biomechanical aspects than ES. This article showed that PSI provides a clinically important adjunct to ES. In the present article, we show that PSI can provide an acceptable index even if a person falls during the trial, whereas ES assigns a zero score for any fall. We also show that PSI decreases as ankle stiffness increases, which is intuitive, while ES exhibits the opposite behavior. Ankle stiffness is generally recognized as an indicator of postural stability. These results suggest that PSI is a more valid measure of A-P stability than ES.

Original languageEnglish (US)
Pages (from-to)547-555
Number of pages9
JournalJournal of Rehabilitation Research and Development
Issue number4
StatePublished - Jul 2005

All Science Journal Classification (ASJC) codes

  • Rehabilitation


  • Ankle stiffness
  • Balance
  • Center of pressure
  • Dynamic posturography
  • Equilibrium score
  • Mathematical model
  • Postural stability
  • Sensory organization test
  • Stabilizing torque
  • Sway angle
  • Sway-referenced motion
  • Two-link model


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