ASTM D4271-88(1994)

This practice provides advice on the preparation of statements on sampling in test methods for textiles. It should be used whenever a new test method is written or when an existing test method needs a revised statement on sampling.

The objective of sampling may vary with the purpose for which the test method is used. The objective of sampling for acceptance testing is to obtain material which will estimate without bias a property of the lot being evaluated and which allows making a decision on whether to accept or reject a lot with reasonable producer’and consumer’risks when the acceptable quality level and the limiting quality level are at realistic levels.

There are normally many ways to estimate the property of interest to a specified degree of precision. The most economical way to do so will depend on the relative size of the sources of variability associated with sampling and the relative cost of sampling the primary sampling units, subunits from within a primary sampling unit, and specimens from within a subunit of a primary sampling unit.

4.3.1 The sources of variability associated with the test method that are estimated by an interlaboratory testing program may be useful in writing statements on the precision of the test method but may not be useful in planning a sampling program. For planning effective sampling procedures, it is necessary to know the sources of variability associated with sampling material of the type that is to be submitted for testing. Estimating such sources of variability normally is done by a nested analysis of variance within the laboratory of the purchaser or supplier or both (2).

When a test method is used in acceptance sampling, the information in the statement of sampling in the test method itself should be supplemented by more specific instructions either in a material specification or in an agreement between the purchaser and the supplier. See Practice D 3777.

Annex A1 gives an explanation and a schematic diagram of the nomenclature used in sampling and testing procedures.

1.1 This practice serves as a guide for preparing statements on sampling in methods of test for textiles. Illustrative texts are included which, with suitable modification, can be used as starting points for writing statements on sampling for any of the usual forms in which textiles are shipped.

1.2 Since the primary purpose of ASTM test methods is to evaluate some characteristic of a material being transferred from a supplier to a purchaser, the procedures for sampling in this practice are directed to the acceptance testing of commercial shipments of a product. Test methods which are not recommended for use in acceptance testing of commercial shipments or which are only intended for ranking products for developmental purposes, may require modifications in the format of the appropriate illustrative text, such as the omission of any reference to lot samples.

1.3 ASTM standards are developed by a consensus process that considers the interests of producers, consumers, and the general public. Committee D13, therefore, recommends giving preference to methods of selecting sampling plans, such as the two-point plans in the annexes in Practice D3777, that require conscious consideration of both the producer's risk and the consumer's risk. The consumer's risk can be determined for the sampling plans in MIL-STD-105D and MIL-STD-414 but those military standards tend to focus attention on the producer's risk rather than on both the producer's and consumer's risks.

1.4 This practice makes no attempt to develop any theoretical basis for sampling. The theoretical basis for sampling is discussed in a number of standard statistical texts (1-5) as well as in Practice E105. Procedures for developing simple two-point single sampling plans for acceptance testing are given in Practice D3777.

1.5 This standard includes the following sections: