ANSI TAPPI T1200 SP-2014 Interlaboratory evaluation of test methods to determine TAPPI repeatability and reproducibility.pdf

1、TAPPI/ANSI T 1200 sp-14 TENTATIVE STANDARD 1961 OFFICIAL STANDARD 1969 RECOMMENDED PRACTICE 1986 REAFFIRMED 1991 REVISED AND COMBINED WITH T 1206 2000 CORRECTION 2006 REVISED 2007 REVISED 2014 2014 TAPPI The information and data contained in this document were prepared by a technical committee of th

2、e Association. The committee and the Association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the m

3、ost recent edition published. Approved by the Standard-Specific Interst Group for this Practice TAPPI CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safe

4、ty issues related to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal,

5、 or both, of chemicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of p

6、otentially hazardous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authoriti

7、es for safe use and disposal of these chemicals. Interlaboratory evaluation of test methods to determine TAPPI repeatability and reproducibility 1. Scope1.1 This practice describes techniques for conducting and analyzing the results of intralaboratory and interlaboratory studies. The steps described

8、 here will result in a good statistical design that provides sound data for formulating a broadly applicable precision statement regarding the performance of a TAPPI test method. 1.2 Two values are considered: (a) repeatability, which is defined as comparison of test results within a laboratory (sam

9、e material, operator, apparatus, environmental conditions, making tests in the shortest reasonable timeframe); and (b) reproducibility, which is defined as comparison of test results among laboratories (same material, but different operator, apparatus and perhaps environmental conditions). 1.2.1 In

10、the data chain leading to test results there are many possible sources of variation, and one can conduct studies to isolate these other sources, e.g. same laboratory and operator using different instruments or different laboratories using a shared calibration standard etc. For the purposes of TAPPI

11、test methods, all of these sources of variation are to be captured in a reproducibility value. 2. Summary of practice 2.1 Reliable data may come from any of the following sources: existing data from a known source with sufficient supporting information, intralaboratory study, or interlaboratory stud

12、y. 2.2 To conduct an interlaboratory study, randomized test specimens of each of several materials are distributed to the participating laboratories, along with appropriate instructions and data sheets. Data returned by the laboratories are analyzed one material at a time. (An assumption that differ

13、ent materials will yield similar precision data is NOT made.) 2.3 Tabular, statistical, and graphical diagnostic procedures are used to estimate averages and variance of the method under question and to show unusual features of the data and patterns among materials that may affect the validity T 120

14、0 sp-14 Interlaboratory evaluation of test methods to / 2 determine TAPPI repeatability and reproducibility or form of the precision statement. 2.4 The information is appropriately summarized in a form from which the precision statement may be readily understood and applied by users of the test meth

15、od. 3. Significance 3.1 The precision statement gives an indication of the level of variability users of a TAPPI test method can expect. Examples of applications of these values are shown in Appendix A.3. 3.2 TAPPI Standards: Regulations and Style Guide requires precision statements in TAPPI Officia

16、l and Provisional Test Methods. Official Test Methods must have both repeatability and reproducibility estimates. Provisional Test Methods must have repeatability estimates. 4. Definitions 4.1 Test determination the value obtained by carrying out the series of operations specified in the test method

17、 whereby readings are made on a test specimen. 4.2 Test result the value obtained for one test unit of the sample. The result is either a single test determination or a specified combination of a number of test determinations (e.g., an average). The method must describe the manner in which each test

18、 determination is to be made, the number of test determinations to be made, and how these determinations must be combined to give the test results. For example, the test method for paper thickness, T 551 “Thickness of paper and paperboard (soft platen method)” requires one determination for each of

19、10 specimen strips; the test result for thickness is defined as the average of these 10 test determinations. 4.3 Repeatability an estimated limit below which the difference between two test results is expected to fall 95% of the time, when the results are obtained at a single laboratory. Repeatabili

20、ty reflects the variability inherent in the experimental system used to determine its value(s). 4.4 Repeatability conditions conditions that reflect the most controlled experimental circumstances possible. Major measurement biasing factors should remain constant including: equipment, operator, test

21、procedure, environmental conditions, sample preparation and in a single testing interval using presumably homogenous samples. 4.5 Reproducibility an estimated limit below which the difference between two test results is expected to fall 95% of the time, when the results are obtained in different qua

22、lified laboratories for the same homogeneous source of material. While each laboratory tests samples taken at random from a single source of material, all of the other factors influencing measurements not considered for repeatability contribute to the variability in the results obtained in different

23、 laboratories. 4.6 Reproducibility conditions conditions that reflect only the most basic control over measurement-influencing factors. Reproducibility conditions should include qualified personnel in qualified laboratories carrying out the same procedure (test method) on different samples of the sa

24、me presumably homogeneous material. Qualified laboratories are those having the required properly calibrated apparatus and environmental conditions and trained personnel who conscientiously follow the prescribed test method (see Section 5.3 for further information). Many of the influences that are c

25、onsidered constant in repeatability are not controlled for reproducibility conditions including: equipment, operator, environmental conditions etc. 4.7 The 95% probability level for both repeatability and reproducibility (4.4 and 4.6) is generally accepted for precision estimations and is also chose

26、n by other standard writing organizations (e.g. ASTM and ISO). Thus TAPPI repeatability and reproducibility can be considered compatible with the precision statistics in methods currently published by ASTM and ISO. Repeatability and reproducibility are different from, but related to, the 95% confide

27、nce interval for a particular test result. Confidence intervals are often estimated by performing replicates and correcting for the number of replicates using Students t test. For more information see: http:/www.itl.nist.gov/div898/handbook/prc/section1/prc14.htm. 4.8 Intralaboratory study a study d

28、esigned to estimate the precision (repeatability) of a test method that meets the requirements of Section 5 and is conducted in a single laboratory. 4.9 Interlaboratory study a study designed to estimate the precision (repeatability and reproducibility) of a test method that meets the requirements o

29、f Section 5 and is conducted at multiple laboratories. 3 / Interlaboratory evaluation of test methods to T 1200 sp-14 determine TAPPI repeatability and reproducibility 5. Planning the intra- or interlaboratory study 5.1 Basic design. Keep the design as simple as possible in order to obtain estimates

30、 that are an accurate reflection of the method in common usage. The basic design is represented by a two-way classification table in which the rows represent the laboratories, the columns represent the materials, and each cell (i.e., the intersection of a row with a column) contains the measurements

31、 made by a particular laboratory on a particular material (Table 1 and Table 3). 5.2 Test method. 5.2.1 The test method should be reviewed to assure that it has been well-written and subjected to careful investigation at one or more competent laboratories to determine clarity and stability. Furtherm

32、ore, it should be easy to follow by any properly equipped laboratory with competent personnel having knowledge of the materials and of the property to be tested. 5.2.2 The method should have a clearly defined numerical result which can be derived from a single determination or a combination of multi

33、ple determinations. The results are assumed to follow a normal distribution. 5.2.3 The method should specify the care of test specimens, including prominent instructions for preconditioning and conditioning when required (see Section 6.2.4). 5.2.4 The method should specify the need for and frequency

34、 of adjustment and calibration of the test apparatus. 5.3 Laboratories. 5.3.1 Any laboratory that would be considered qualified to run the test in routine testing situations is permitted and encouraged to participate in the interlaboratory study, but the number of laboratories may be restricted if t

35、here is a large amount of work involved in preparing samples or there is a significant increase in sampling variability due to the larger amount of material required. 5.3.2 Laboratories must be properly equipped to follow all details of the procedure and be willing to assign the work to a skilled op

36、erator on a timely basis. The decision of a laboratory to participate should be based on information provided by the working group, including information as to the required time for calibrating the apparatus and for testing all of the materials. 5.3.3 Subject to the conditions in 5.3.1 and 5.3.2, us

37、e as many laboratories as practical, preferably 20 to 30. Because of the possible loss of data from some laboratories for some materials, it is highly desirable to include at least eight laboratories to obtain a usable estimate of the reproducibility of the test method. In consideration of the refer

38、ee nature of TAPPI test methods, more than a mere usable estimate of the reproducibility between laboratories is highly desirable. Because the data required from each laboratory are held to a minimum in this practice, to encourage the participation of an adequate number of laboratories. Under no cir

39、cumstances should a precision statement be based on an interlaboratory trial with fewer than five laboratories. 5.3.4 Avoid restricting the study to a group of laboratories judged to be exceptionally qualified and equipped. Precision estimates for inclusion in a TAPPI test method should be obtained

40、through the efforts of laboratories and personnel operating under conditions that are representative of the situations in which the test method will be used in practice. 5.4 Materials. 5.4.1 Number and types. The number and types of materials to be included in the interlaboratory study should (1) sp

41、an the range of the values of the property being measured, (2) span the number of scales to cover the range if the instrument has more than one scale, and (3) reflect the number of types or classes of materials to which the test method is to be applied. If the precision trial is restricted in any of

42、 these areas, the omitted information must be noted in the precision statement. 5.4.2 Without previous knowledge concerning the behavior of different classes of material subject to the method, it should be assumed that different materials will exhibit different performance characteristics. When a me

43、thod covers different classes of materials, it may be desirable to conduct separate trials to suit the expertise of the laboratories involved. Thus the selected materials within each class differ from each other only in level and should not pose difficulties to the participating laboratories. 5.5 Re

44、plicates. 5.5.1 If the test method defines a test result as the average of a set number of test determinations, the study should consist of at least three times that number of replicate determinations. 5.5.2 If the test method requires a recalibration or some other special procedure between each tes

45、t result but not between each test determination, each replicate in the study must be a complete test result, and at least three replicate results should be obtained T 1200 sp-14 Interlaboratory evaluation of test methods to / 4 determine TAPPI repeatability and reproducibility 6. Conducting an intr

46、a- or interlaboratory study 6.1 The working group should prepare a protocol for the participants in the study, which should include detailed instructions for the following: 6.1.1 Any exception to or selection of the test procedure as specified in the test method. Expected date of the testing, especi

47、ally if the aging of samples may be important (see 6.2.3); 6.1.3 Any special circumstances that must be addressed in implementing the repeatability conditions (one operator, one apparatus, shortest time span); 6.1.4 The recording of measurements, including the number of decimal places to be used, wh

48、ich, when possible, should be one more than is required to be reported by the test method under study in order to allow reliable calculation of the precision of the method; 6.1.5 The keeping of a log of unusual events that arise during any phase of the testing; 6.1.6 Notifying the study coordinator

49、when an error in test procedure arises so that replacement test specimens may be sent. 6.2 Sampling and sample preparation and distribution. 6.2.1 Sampling of materials. 6.2.1.1 Sample each material so that the variability among the specimens of that material will be minimized. 6.2.1.2 Prepared in accordance with the sampling section of the method, if applicable. 6.2.1.3 For samples of paper, take all specimens from a small area of a single roll, avoiding the edges of the roll. Usually, specimens taken adjacent to each other in the machine direc