1. A method comprising: Providing a motion capture apparatus in communication with a processor operable to capture three-dimensional video and data representations of a subject on a frame-by-frame basis; locating said subject in front of said motion capture apparatus; having said subject sequentially maintain each posture of a plurality of predetermined sequential stationary postures, each said posture being maintained by said subject for one of a predetermined period of time, the occurrence of a postural event, and the occurrence of a postural stability event; utilizing said motion capture apparatus to capture simultaneous frame-by-frame video and data representations of said subject while said subject maintains each posture of said plurality of predetermined sequential stationary postures; calculating a subject center of gravity (COG) for each frame of said frame-by-frame subject positional data representation; selecting for each said posture of said plurality of predetermined sequential stationary postures a COG for a predetermined frame of data as a reference COG for said posture; utilizing said reference COG to determine a reference vector for each said posture of said plurality of predetermined sequential stationary postures; utilizing each said subject COG for each said frame of data to calculate a frame vector; determining and storing a sway angle between said reference vector and each said frame vector; determining standard deviations of each said sway angle to represent a sway index angle for each posture.