A program for assuring the quality of products made from plastics is only as valid as the test methodology that supports it. Test methods can be characterized as to their repeatability and reproducibility. Both of these measures describe the level of precision, or agreement among test results, obtained when a test method is used to characterize a product, be it a raw material or a finished part. ASTM requires that each test method in the ASTM Book of Standards be provided with a statement of precision and accuracy. This paper describes some recent efforts within Committee D20 on Plastics to assess the precision of two test methods. The results are analyzed using ASTM Practice for Conducting an Interlaboratory Test Program to Determine the Precision of a Test Methods (E 691).

The implications of the measured precision of the test methods for their use in quality assurance activities are described.