Price Survey of Assistive Devices and Supports for Persons with Disabilities - December 2003

Tests Utilized in Choosing to Report Average Prices

The following tests were applied to price data where 10 or more but 25 or less prices were obtained for a given product:

1. Coefficient of Variation (CV) test:
   Where less than 16.5% prices are reported without an asterisk.
   1. Those with a coefficient of variation between 16.6% and 33.3% are reported with an asterisk. Caution is to be used in reporting on these prices because of higher levels of sample variance.
   2. Where CV was greater than 33.3% data was not reported.
2. Skewness test: the absolute value Hildebrand measure was used:
   Absolute (estimated. mean — estimated median divided by estimated. standard deviation).
   1. where less than .2, no asterisk is added.
   2. where equal to .2 but less than .4 an asterisk is added. This indicates that the data has a moderate skew.
   3. Where the measure is greater than .4, the statistic is not reported.
      Note: using the Pearsonian measure of skewness and values of absolute 1 and 2 yield similar results.
3. Kurtosis Test:
   1. Where between -2 and 2, no asterisk is added.
   2. Where greater than 2 but less than 4 an asterisk is added indicating that the distribution is flatter than a normal distribution.
   3. Where greater than 4, the mean is not reported, since there is not a high degree of "central tendency" in the distribution.

Tests were applied to the price distributions of the following products:

• Text Telephone Device (with display only)
• Vibro Tactile Full Function Alarm
• Shoulder-Elbow-Wrist-Hand-Finger Orthosis
• All Prostheses
• Scooter/Wheelchair Acid Battery
• Porch Lift
• Chair Lift
• Elevator
• Bi-level CPAP Device
• Glucometer Test Strips

Because of the nature of the data collected, the tests could not be applied to van/automobile conversion data or data concerned supports for the blind/persons with severe sight impairment.