SIST-TS ISO/TS 16489:2010

TECHNICAL ISO/TS
SPECIFICATION 16489
First edition
2006-05-15
Water quality — Guidance for
establishing the equivalency of results
Qualité de l'eau — Lignes directrices pour la création de l'équivalence
des résultats
Reference number
©
ISO 2006
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ii © ISO 2006 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Overview of the different approaches .2
5 Amount of data.2
6 Data comparisons.3
7 Comparison of arithmetic means of two independently obtained sets of data .3
8 Comparison of population and sample arithmetic means .4
9 Analysis of variance .5
10 Determination of the equivalence of analytical results obtained from samples from
different matrices.7
10.1 General.7
10.2 Determination of the equivalence of the analytical results of real samples using
orthogonal regression.7
10.3 Evaluation according to the difference method .9
11 Reporting .10
Annex A (informative) Statistical tables.11
Annex B (informative) Example of a comparison of arithmetic means of two independently
obtained sets of data.13
Annex C (informative) Example of a comparison of population and sample arithmetic means.15
Annex D (informative) Example of an analysis of variance .16
Annex E (informative) Examples of a comparison of results from samples of different matrices.18
Annex F (informative) Illustrative examples of graphic plots.24
Annex G (informative) Schematic diagrams.27
Bibliography .29

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
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International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
⎯ an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
⎯ an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
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International Standard or be withdrawn.
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.
ISO/TS 16489 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2,
Physical, chemical and biochemical methods.
iv © ISO 2006 – All rights reserved

Introduction
The methods referred to in this Technical Specification can comprise a standard or reference method, the
results of which are to be compared with results generated by an alternative, perhaps more simple, method.
Alternatively, a comparison of results produced by an old established method and those produced by a new
more modern technique can be undertaken. The methods can be laboratory based or undertaken “on-site”
where the samples are taken.
No indication is given to confirm whether either one of the two methods, in terms of bias, is better or worse
than the other method, only that the results produced by both methods are considered equivalent or not, in
terms of the calculated means, standard deviations and variances. The procedures described are not to be
used for, and do not apply to, situations to establish whether two methods can be shown to be equivalent. The
procedures apply only to demonstrating equivalency of results.
Since standard deviations and means can vary with concentrations, especially where concentrations vary over
several orders of magnitude, the procedures described in Clauses 7 to 9 are only applicable to samples
containing a single level of concentration. It would be necessary to repeat the procedures for each
concentration level if different concentration levels are encountered, and it is shown that standard deviations
and means vary over these concentration levels. It might be that the demonstration of equivalence can only be
achieved over relatively small concentration ranges. For multiple concentration levels, the procedures
described in Clause 10 might be applicable. In addition, the laboratory will need to show that both methods
are suitable and appropriate for the sample matrix and the parameter under investigation, including the level
of concentration of the parameter. Also, the experimental data obtained in the comparison of results should
reflect the specific application for which equivalence is questioned, as different matrices can lead to different
results with the two methods.
Throughout this Technical Specification, it is assumed that results are obtained essentially under repeatability
conditions, but it is recognized that this will not always be so. Hence, where appropriate, identical samples are
analysed by the same analyst using the same reagents and equipment in a relatively short period of time.
Furthermore, a level of confidence of 95 % is assumed. The statistical tests described in this Technical
Specification assume that the data to be compared are independent and normally distributed in a Gaussian
manner. If they are not, the data might not be suitable for the statistical treatments described and additional
data might need to be collected.
The power of the statistical test is greatly enhanced when sufficient data are available for comparisons; i.e.
when the numbers of degrees of freedom are available to enable a meaningful interpretation to be made.
However, it is recognized that a statistically significant difference might not necessarily infer an important or
meaningful difference, and a personal judgement should be made on whether a statistically significant
difference is important or meaningful and relevant. Alternatively, a statistical test might not be sufficiently
powerful to be able to detect a difference that from a practical point of view could be regarded as important or
meaningful.
To aid the analyst, advice is provided as to which clause (and corresponding annex) is applicable to the
circumstances surrounding the data that have been generated. It is recognized that when results are
compared they can have been generated under a variety of different conditions.

TECHNICAL SPECIFICATION ISO/TS 16489:2006(E)

Water quality — Guidance for establishing the equivalency
of results
1 Scope
This Technical Specification describes statistical procedures to test the equivalency of results obtained by two
different analytical methods used in the analysis of waters. This Technical Specification is not applicable for
establishing whether two methods can be shown to be equivalent. The procedures given in this Technical
Specification are only applicable to demonstrating the equivalency of results.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method
for the determination of repeatability and reproducibility of a standard measurement method
NOTE A practical guidance document to assist in the use of ISO 5725-2 has been published: see ISO/TR 22971.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply:
3.1
precision
closeness of agreement between independent test results obtained under repeatability conditions
NOTE 1 Precision depends only on the distribution of random errors and does not relate to the true, specified or
accepted value.
NOTE 2 Measurement of precision is usually expressed in terms of imprecision and computed as a standard deviation
of the test results. Less precision is reflected by a larger standard deviation.
NOTE 3 “Independent test results” means results obtained in a manner not influenced by any previous result on the
same sample. Quantitative measurements of precision depend critically on stipulated conditions.
3.2
repeatability conditions
conditions where independent test results are obtained with the same method on identical test samples in the
same laboratory, by the same operator, using the same reagents and equipment within short intervals of time
3.3
analytical method
unambiguously written procedure describing all details required to carry out the analysis of the determinand or
parameter, namely: scope and field of application, principle and/or reactions, definitions, reagents, apparatus,
analytical procedures, calculations and presentation of results, performance data and test report
4 Overview of the different approaches
Where a sample is analysed in replicate using two methods, then the procedures described in Clause 7 and
Annex B may be used. The results should, ideally, be generated by a single analyst, however, it is re
...