Accuracy (trueness and precision) ofmeasurement methods and results - Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method
1.1 This Part of GB/T 6379
― amplifies the general principles to be observed in designing experiments for the numerical estimation of the precision of measurement methods by means of a collaborative interlaboratory experiment;
― provides a detailed practical description of the basic method for routine use in estimating the precision of measurement methods;
― provides guidance to all personnel concerned with designing, performing or analyzing the results of the tests for estimating precision.
Note 1: Modifications to this basic method for particular purposes are given in other parts of GB/T 6379.
Appendix B provides practical examples of estimating the precision of measurement methods by exper?iment.
1.2 This Part of GB/T 6379 is concerned exclusively with measurement methods which yield measurements on a continuous scale and give a single value as the test result, although this single value may be the outcome of a calculation from a set of observations.
1.3 It assumes that in the design and performance of the precision experiment, all the principles as laid down in GB/T 6379.1 have been observed. The basic method uses the same number of test results in each laboratory, with each laboratory analyzing the same levels of test sample; i.e. a balanced uniform-level experiment. The basic method applies to procedures that have been standardized and are in regular use in a number of laboratories.
Note 2: Worked examples are given to demonstrate balanced uniform sets of test results, although in one example a variable number of replicates per cell were reported (unbalanced design) and in another some data were missing. This is because an experiment designed to be balanced can turn out to be unbalanced. Stragglers and outliers are also considered.
1.4 The statistical model of Chapter 5 of GB/T 6379.1-2004 is accepted as a suitable basis for the interpretation and analysis of the test results, the distribution of which is approximately normal.
1.5 The basic method, as described in this Part of GB/T 6379, will (usually) estimate the precision of a measurement method:
a) when it is required to determine the repeatability and reproducibility standard deviations as defined in GB/T 6379.1;
b) when the materials to be used are homogeneous, or when the effects of heterogeneity can be included in the precision values;
c) when the use of a balanced uniform-level layout is acceptable.
1.6 The same approach can be used to make a preliminary estimate of precision for measurement methods which have not reached standardization or are not in routine use.
Foreword II
Introduction III
1 Scope
2 Normative References
3 Definitions
4 Estimates of the Parameters in the Basic Model
5 Requirements for a Precision Experiment
5.1 Layout of the experiment
5-2 Recruitment of the laboratories
5.3 Preparation of the materials
6 Personnel Involved in a Precision Experiment
6.1 Panel
6.2 Statistical functions
6-3 Executive functions
6.4 Supervisors
6.5 Operators
7 Statistical Analysis of a Precision Experiment
7.1 Preliminary considerations
7.2 Tabulation of the results and notation used
7.3 Scrutiny of results for consistency and outliers
7.4 Calculation of the genera! mean and variances
7.6 Statistical analysis as a step-by-step procedure
7.7 The report to, and the decisions to be taken by, the panel
8 Statistical Tables
Appendix A (Normative) Symbols and Abbreviations Used in GB/T 6379
Appendix B (Informative) Examples of the Statistical Analysis of Precision Experiments
B.1 Example 1: Determination of the sulfur content of coal (Several levels with no missing or outlying data)
B.2 Example 2: Softening point of pitch (Several levels with missing data)
B.3 Example 3; Thermometric titration of creosote oil (Several levels with outlying data)
Appendix C (Informative) Bibliography
