Poor postural stability of the elderly and other patients has been a major concern.The cost of treating injuries due to poor stability is expected to rise to $32.4 Billion by 2020. Many interventions have been proposed and used to improve stability. In order to determine the efficacy of these interventions, an objective evaluation of postural stability before and after intervention is important.

The aim of this thesis was to scientifically analyze the ambiguities in the equilibrium score (ES) given by the Neurocom Smart Equitest (NSE) machine, and compare it to a new measure of stability that has been proposed by Chaudhry et al., (2003) the postural stability index (PSI). This was done by determining the correlation of PSI and ES between the average sway angle, the ankle stiffness, and the SF-36 summary scores. Another aim was to investigate a method of validating mathematical models of the postural system, with the help of Ascension's Flock of Birds (FOB). This was done by testing the position output of the FOB in the NSE environment.

It was found that the average sway angle and ankle stiffness correlates better with the PSI. However, the SF-36 summary scores correlates better with the ES although both have poor correlation. It was also found that the FOB had a maximum error of 2.5 inches over a height range of 15.5 to 40.5 inches.