where r is the random variable (in this case, the uniform probability distribution) and [omega] is the width of the class interval about the quantised variable x in the
step wedge. This operation produces a random scatter plot suitable for regression analysis.
Concerning the radiopacity of materials, the International Organization for Standardization has stated that radiopacity is evaluated using the aluminum
step wedge technique with a range of 0.5-5.0 mm thickness at 0.5 mm increments at an accuracy of >98% purity and 0.05 mm variation in thickness [17].
Optical density means were calculated based on the measurements taken in three different areas of each sample and on the fifth step of the
step wedge (which corresponded to 5 mm).
The films were exposed to an optical
step wedge created by a software program built into the Kodak Dry View 8300 unit (Kodak, Rochester, New York).
X-ray machines are also submitted by their manufacturers to be certified as meeting certain standards - most notably the ASTM
Step Wedge Test.