This practice describes techniques for conducting intra-laboratory and interlaboratory studies, analyzing the results of intra-laboratory and interlaboratory studies and the formulation of appropriate precision statements for TAPPI test methods. The techniques recommended have the primary purpose of providing reliable information on the basis of which a broadly applicable precision statement can be made regarding the performance of a TAPPI test method.
To achieve the above objective satisfactorily, it is essential that a sound statistical design be employed in the planning of an interlaboratory study. Two situations are considered: (a) repeatability or comparison of test results within a laboratory (same material, operator, apparatus, environmental conditions, making tests in the shortest reasonable timeframe); and (b) reproducibility or comparison of test results among laboratories (same material, but different operator, apparatus and perhaps environmental conditions). There are a multitude of intermediate measures of precision, e.g. same laboratory and operator using different instruments or different laboratories using a shared calibration standard etc., which are not covered in this standard.
Other situations within a laboratory are not considered, e.g., data collected by all operators, or on all apparatus, or on different occasions when different environmental conditions might prevail. Because the agreement among the values obtained in these situations depends on the degree of supervision and control exercised in that laboratory, statements of precision about these situations are not appropriate in a test method for general use.
