ASTM D6300 Precision and Bias Data for Use in Test Methods for Petroleum Products and Lubricants
ASTM D6300 Standard Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products and Lubricants
4. Summary of Practice
4.1 A draft of the test method is prepared and a pilot program can be conducted to verify details of the procedure and to estimate roughly the precision of the test method.
4.2 A plan is developed for the interlaboratory study using the number of participating laboratories to determine the number of samples needed to provide the necessary degrees of freedom. Samples are acquired and distributed. The interlaboratory study is then conducted on an agreed draft of the test method.
4.3 The data are summarized and analyzed. Any dependence of precision on the level of test result is removed by transformation. The resulting data are inspected for uniformity and for outliers. Any missing and rejected data are estimated. The transformation is confirmed. Finally, an analysis of variance is performed, followed by calculation of repeatability, reproducibility, and bias. When it forms a necessary part of the test procedure, the determinability is also calculated.
5. Significance and Use
5.1 ASTM test methods are frequently intended for use in the manufacture, selling, and buying of materials in accordance with specifications and therefore should provide such precision that when the test is properly performed by a competent operator, the results will be found satisfactory for judging the compliance of the material with the specification. Statements addressing precision and bias are required in ASTM test methods. These then give the user an idea of the precision of the resulting data and its relationship to an accepted reference material or source (if available). Statements addressing determinability are sometimes required as part of the test method procedure in order to provide early warning of a significant degradation of testing quality while processing any series of samples.
5.2 Repeatability and reproducibility are defined in the precision section of every Committee D-2 test method. Determinability is defined above in Section 3. The relationship among the three measures of precision can be tabulated in terms of their different sources of variation (see Table 1). 5.2.1 When used, determinability is a mandatory part of the Procedure section. It will allow operators to check their technique for the sequence of operations specified. It also ensures that a result based on the set of determined values is not subject to excessive variability from that source.
5.3 A bias statement furnishes guidelines on the relationship between a set of test results and a related set of accepted reference values. When the bias of a test method is known, a compensating adjustment can be incorporated in the test method.
5.4 This practice is intended for use by D-2 subcommittees in determining precision estimates and bias statements to be used in D-2 test methods. Its procedures correspond with ISO 4259 and are the basis for the Committee D-2 computer software, Calculation if Precision Data: Petroleum Test Methods. The use of this practice replaces that of Research Report D02:1007.
5.5 Standard practices for the calculation of precision have been written by many committees with emphasis on their particular product area. One developed by Committee E-11 on Statistics is Practice E 691. Practice E 691 and this practice differ as outlined in Table 2.
