biodex BioSway Operation Manual page 44

X
Standard deviation (Sd)
This is the amount of variability in the statistical measure between data points. A low standard
deviation demonstrates that the range of values from which the mean was calculated were close
together. Standard Deviation should be relatively low.
∑ √(Xn – X) 2
n____________
n
data InterpretatIon for the lImItS of StabIlIty
Since the BioSway measures COG angular displacement from center it can be used to assess a
patient's LOS in two ways.
method 1
Using the Stability Index (SI) gained from a Dynamic Balance Report it can be determined how
well a patient controls their balance within their LOS in both an Anterior/Posterior (A/P) direc-
tion and a Medial/Lateral direction (M/L). For example, an A/P SI of 6.8 would mean that a
patient remains within 57% of their A/P LOS:
therefore: 6.8/12 = .566 or .57 x 100 = 57%
The same method can be used to determine the M/L LOS control. They are both important for
determining a patient's potential risk for falling. Rehabilitation exercises can be properly pre-
scribed from these results to effectively assist the patient to better control their LOS.
method 2
By using the Limits of Stability Test protocol it can be determined exactly in which direction a
patient may have more trouble controlling their LOS. The test results are based on 100, with 100
being a perfect score. The patient's score is based on their ability to accurately move the display
cursor to a target 10 º from a level platform position and back to level again. The more direct the
path to the target and back to center the higher their score will be. Lower Scores may be indica-
tive of poor neuromuscular control.
Parameters for this Assessment can be found on the report for the Comprehensive LOS. Test
report. The formula found below is used to calculate the final score which is represented both
numerically and graphically. From the results it can be determined how well the subject was
able to control their COG over their BOS. Higher numbers represent better control, with lower
numbers representing a poor control. The report also gives the total time it took the patient to
complete the test which can also be compared between sessions.
REPORTS AND DATA
n = # of samples
Xn = n th sample
X = mean deflection
A/P LOS = 12
A/P SI = 6.8
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