Reliability and validity of the Sway Balance mobile application for measurement of postural sway in people with Parkinson disease.

BACKGROUND: The emergence of mobile technology allows the examination of balance through direct measures of postural sway in a cost-effective, convenient and portable fashion. However, there is insufficient evidence for use in populations with neurologic conditions.

OBJECTIVES: 1) To determine the test-retest reliability of the Sway Balance™ mobile application in measuring postural sway in individuals with Parkinson disease, 2) To examine the concurrent validity of Sway Balance™ with inertial measurement units and 3) To determine if Sway Balance™ scores can predict disease severity.

METHODS: Thirty subjects with early stage idiopathic Parkinson disease completed three trials of two Sway Balance™ protocols while postural sway was simultaneously measured by two inertial measurement units and Sway Balance™, then repeated testing one week later.

RESULTS: Sway Balance demonstrated high test-retest reliability for both protocols (ICC = 0.72 and 0.92) and good to excellent inverse correlation with the inertial measurement units across both protocols (ρ= -0.61- -0.92; p < 0.001). Sway Balance™ did not accurately predict disease severity.

CONCLUSION: Sway Balance™ demonstrates strong test-retest reliability and concurrent validity with measures from inertial measurement units. Questions remain regarding the ability of Sway Balance™ to accurately characterize balance of individuals who demonstrate difficulty maintaining the test condition.