The procedures in these test methods may be used for the acceptance testing of commercial shipments, but caution is advised because technicians may fail to get good agreement between results on certain yarns, cords, or fabrics. Comparative tests as directed in Section 5.1.1 may be advisable.

If there are differences of practical significance between reported test results for two laboratories (or more), comparative tests should be performed to determine if there is a statistical bias between them, using competent statistical assistance. As a minimum, test samples should be used that are as homogeneous as possible, that are drawn from the material from which the disparate test results were obtained, and that are randomly assigned in equal numbers to each laboratory for testing. Other materials with established test values may be used for this purpose. The test results from the two laboratories should be compared using a statistical test for unpaired data, at a probability level chosen prior to the testing series. If a bias is found, either its cause must be found and corrected, or future test results for that material must be adjusted in consideration of the known bias.

The significance and use of particular properties are discussed in the appropriate sections of the specific test methods.