ISO/TR 24498:2019

TECHNICAL ISO/TR
REPORT 24498
Second edition
2019-01
Paper, board and pulps — Estimation
of uncertainty for test methods by
interlaboratory comparisons
Papiers, cartons et pâtes — Estimation de l'incertitude pour les
méthodes d'essai par comparaisons interlaboratoires
Reference number
ISO/TR 24498:2019(E)
©
ISO 2019

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ISO/TR 24498:2019(E)

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© ISO 2019
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Published in Switzerland
ii © ISO 2019 – All rights reserved

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ISO/TR 24498:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Procedure. 2
5 Preparation of an interlaboratory study . 3
5.1 Laboratories . 3
5.1.1 Qualification of laboratories . 3
5.1.2 Number of participating laboratories . 3
5.2 Sample preparation and distribution . 3
5.2.1 Number and type of material . 3
5.2.2 Selection of the material. 3
5.2.3 Identification and packaging . 4
5.2.4 Additional and specific care . 5
5.3 Documentation for the interlaboratory study . 5
6 Recommendations for testing . 5
7 Analysis of the results . 6
7.1 Calculations . 6
7.2 Case of interlaboratory study organised by the working group. 6
7.2.1 General. 6
7.2.2 Consistency evaluation . 7
7.2.3 Handling of outlying data . 7
7.3 Case of data provided from proficiency testing services . 7
8 Re-evaluation of the uncertainty . 8
9 Report . 8
10 Archiving raw data . 8
Annex A (informative) Tappi and ISO codifications . 9
Annex B (informative) Example of a recommended form to be distributed to participating
laboratories for the collation of results for analysis .10
Annex C (informative) Example of precision statements for physical properties.11
Bibliography .12
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ISO/TR 24498:2019(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.
This second edition cancels and replaces the first edition (ISO/TR 24498:2006), which has been
technically revised. The following changes were made:
— The scope has been modified as the revised document presents guidelines for a methodology for
the estimation of the uncertainty of methods for testing the properties of pulp, paper, board and
cellulosic nanomaterials.
— 2.1 and 2.2 have been moved into the Introduction.
— 2.3 has been moved into the Bibliography.
— Terms and definitions have been updated.
— Clauses 4, 5 and 6 have been entirely revised.
— New information has been introduced regarding procedure, preparation of an interlaboratory
study, including information on the participating laboratories, sample preparation and distribution
and documentation for the interlaboratory study.
— Specifications for cellulosic nanomaterials and for microbiological tests have been introduced.
— 7.3, Clauses 8, 9, 10 and Annexes A and C have been updated.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
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ISO/TR 24498:2019(E)

Introduction
One step in the development of any new standard test method is to estimate the uncertainty of the
method. After such a procedure, a "Precision statement" is usually included in ISO test methods for pulp,
paper and board and is recommended by ISO/TC 6 for all new and revised ISO/TC 6 standards. This is
normally performed in a precision experiment, in which samples are sent to a number of laboratories
and the results are compared. Such a precision experiment is often referred to as "interlaboratory
comparative testing".
[1]
The procedures for conducting a precision statement are outlined in the ISO 5725 series , which is
general and does not cover the special conditions that apply in the testing of pulp, paper, board and
cellulosic nanomaterials (this is the reason why some countries have published national standards or
[2][3][4]
test methods dedicated to pulp, paper and board ).
For example, paper and board materials as well as cellulosic nanomaterials are very sensitive to changes
in relative humidity and temperature. Changes in the environmental conditions may induce significant
moisture content variations in paper and board, which may induce changes in physical and mechanical
properties.
Due to product heterogeneity, randomisation of the samples and /or test pieces is essential to minimize
the impact of such variability. For the same reason, the variation in the properties can increase
drastically when the test piece size decreases, for example when measuring grammage or Cobb water
absorptiveness.
Furthermore, many tests carried out on pulp, paper, board or cellulosic nanomaterials are destructive.
In such cases, it is impossible to achieve a true repeatability measurement.
These reasons make it necessary to have special instructions for precision experiments for pulp, paper,
board and cellulosic nanomaterials.
One effect of the heterogeneity of the product is that a large number of measurements is required in
order to achieve sufficient precision. Most standardized test methods are therefore based on 10 or
more measurements. The result is generally the average of these measurements.
There are four main purposes for testing:
— Research, where the main question is whether there is an expected maximum difference between
two samples, for instance, papers produced using different pulp mixtures.
— Verification of conformance with a specification. This can be at the production central testing
laboratory site or in an independent laboratory.
— Evaluation of a new test method, where the aim is to verify that the precision of the test method is
acceptable.
— Determination of a precision statement for an existing test method either where one does not exist
or where it requires revision.
When the uncertainty of a test method is to be expressed, the following aspects should be considered.
— The conditions for the tests. Are the conditions as similar as possible, or as different as possible?
— The uncertainty can be expressed in different statistical measures, as a standard deviation or as a
confidence interval.
— The uncertainty can be expressed either as a variation in the test results themselves, or as the
difference between two test results.
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TECHNICAL REPORT ISO/TR 24498:2019(E)
Paper, board and pulps — Estimation of uncertainty for
test methods by interlaboratory comparisons
1 Scope
This document presents guidelines for a methodology for the estimation of the uncertainty of methods
for testing pulps, paper, board, cellulosic nanomaterials, and lignins, as well as products thereof
containing any portion of recycled material or material intended for recycling.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
interlaboratory comparison
organization, performance and evaluation of measurements or tests on the same or similar items by
two or more laboratories in accordance with predetermined conditions
[SOURCE: ISO 13528:2015, 3.1]
3.2
interlaboratory test
series of measurements of one or more quantities performed independently by a number of laboratories
on samples of a given material
[SOURCE: ISO 11459:1997, 3.16]
3.3
repeatability conditions
observation conditions where independent test results are obtained with the same method on test
pieces from the same specimen in the same laboratory by the same operator using the same equipment
within a short interval of time
Note 1 to entry: Repeatability conditions are not fulfilled in the procedure described in this document. It is
assessed by the average standard deviation within laboratories instead of a strict repeatability study.
[SOURCE: ISO 3534-2:2006, 3.3.6, modified — "identical test/measurement items in the same test or
measuring facility" has been replaced with "test pieces from the same specimen in the same laboratory";
the Note has been deleted and Note 1 to entry has been added.]
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ISO/TR 24498:2019(E)

3.4
repeatability limit
r
value less than or equal to which the absolute difference between two test results obtained under
repeatability conditions is expected to be with a probability of 95 %
[SOURCE: ISO 3534-2:2006]
3.5
repeatability standard deviation
standard deviation of test results obtained under repeatability test conditions
[SOURCE: ISO 3534-2:2006]
3.6
reproducibility conditions
conditions where the test results are obtained with the same method on test pieces from a sample in
different laboratories with different operators using different equipment
[SOURCE: ISO 3534-2:2006]
3.7
reproducibility limit
R
value less than or equal to which the absolute difference between two test results obtained under
reproducibility conditions is expected to be with a probability of 95 %
[SOURCE: ISO 3534-2:2006]
3.8
reproducibility standard deviation
standard deviation of test results obtained under reproducibility test conditions
[SOURCE: ISO 3534-2:2006]
3.9
uncertainty
non-negative parameter which characterizes the variability in the values obtained
from measurements
[SOURCE: JCGM 200:2012, 2.26, modified]
4 Procedure
The preferred procedure is for an expert from the working group responsible for developing an ISO
Standard to organize the interlaboratory testing while the standard is being developed
In these conditions, tests are performed with commercially available materials, as uniform and stable
as possible, utilizing test instruments which are also available on the market and in the participating
laboratories. A call for participation of laboratories outside of the working group may be permitted.
In the case where an interlaboratory test cannot be implemented by the working group, the use of
comparative testing services data (for example from pulp and paper, collaborative testing services
round robins, or CEPI Comparative Testing Service) are recommended. In this case, the most recent
data should be provided and recalculated in the format used in the ISO/TC 6 standards.
And if neither of the two first options is possible, bibliographic data should be reported.
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ISO/TR 24498:2019(E)

5 Preparation of an interlaboratory study
5.1 Laboratories
5.1.1 Qualification of laboratories
Any laboratory that would be considered qualified to run the test is permitted and encouraged to
participate in the interlaboratory study.
Laboratories should be properly equipped to follow all details of the procedure, including climate
conditions when specified, and be willing to assign the work to a skilled operator on a timely basis with
competent personnel having knowledge of the materials and of the property to be tested.
In many situations it is preferable that participating laboratories meet the requirements of ISO/
[10]
IEC 17025 or equivalent, or that at least they participate in a comparative testing service and have
been shown to be competent in the test for which the precision data is being obtained.
The decision on permitting a laboratory to participate should be based on information provided to
the working group, including information as to the required time for calibrating the apparatus and for
testing all of the materials.
5.1.2 Number of participating laboratories
It is recommended to include at least eight laboratories to obtain a valid estimate of the uncertainty
associated with the test method.
No interlaboratory round robin test should be performed with less than five laboratories.
5.2 Sample preparation and distribution
5.2.1 Number and type of material
The number and types of materials to be included in the interlaboratory study should cover the range
of the values of the property being measured and be representative of the number of types or classes
of materials to which the test method is to be applied. It also should cover each scale of the instrument
(e.g. Scott Bond) if applicable.
If the interlaboratory study is restricted in any of these areas, the omitted information should be
reported in the precision statement.
5.2.2 Selection of the material
5.2.2.1 General
The sampling procedure should be appropriate to the property to be assessed and the type of material
(pulp, paper, board or cellulosic nanomaterial).
It is up to the person responsible for the interlaboratory study to check if the material selected is
suitable or not. If not, the material should be changed.
It is also up to the person responsible for the interlaboratory study to check if the property is normally
distributed. When normality of distribution cannot be proven, it is advised to group the data. One can
also use comparability techniques, i.e. to compare the average mean differences between laboratories,
once the consistency of data coming from these laboratories is also proven graphically.
Each selected product should be sampled so that the variability among the spec
...