CEN/TR 10345:2013

SLOVENSKI STANDARD
01-julij-2014
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SIST-TP CEN/TR 10345:2008
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Guideline for statistical data treatment of inter laboratory tests for validation of analytical
methods
Richtlinien für die Behandlung von statistischen Daten von verschiedenen Laboren für
die Validierung von Analysenverfahren
Guide pour le traitement statistique des données de validation de méthodes d'analyse,
issues d'essais interlaboratoires
Ta slovenski standard je istoveten z: CEN/TR 10345:2013
ICS:
03.120.30 8SRUDEDVWDWLVWLþQLKPHWRG Application of statistical
methods
77.080.01 Železne kovine na splošno Ferrous metals in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 10345
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
December 2013
ICS 17.020; 03.120.30 Supersedes CEN/TR 10345:2008
English Version
Guideline for statistical data treatment of inter laboratory tests for
validation of analytical methods
Guide pour le traitement statistique des données de Richtlinien für die Behandlung von statistischen Daten von
validation de méthodes d'analyse, issues d'essais verschiedenen Laboren für die Validierung von
interlaboratoires Analysenverfahren

This Technical Report was approved by CEN on 29 July 2013. It has been drawn up by the Technical Committee ECISS/TC 102.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 10345:2013 E
worldwide for CEN national Members.

Contents Page
Foreword .3
1 Scope .4
2 Normative references .4
3 Principle .4
4 Preliminary rules .4
5 Procedure .6
6 Report .9
7 General remarks.9
Annex A (normative) Steps for the validation of a draft Standard . 10
Annex B (normative) Synoptic of the operations described in Annex A . 13
Annex C (informative) Examples . 18
Bibliography . 44

Foreword
This document (CEN/TR 10345:2013) has been prepared by Technical Committee ECISS/TC 102 “Methods
of chemical analysis of iron and steel”, the secretariat of which is held by SIS.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes CEN/TR 10345:2008.
In comparison with the previous version of CEN/TR 10345, the following significant technical change was
made in Annex A: correction of the error in the last sentence of A.2 concerning the appropriate number of
significant figures.
1 Scope
This Technical Report is a guideline to carry out the statistical evaluation of data from an inter laboratory test
for method validation.
Its purpose is to detail the methodology of ISO 5725-1:1994, ISO 5725-2:1994 and ISO 5725-3:1994 for the
treatment of the data collected under the conditions used within the ECISS/TC 102 working groups.
NOTE The present document is not a simplification of the ISO 5725 standard, which is the only reference document.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 5725-1:1994, Accuracy (trueness and precision) of measurement methods and results — Part 1: General
principles and definitions
ISO 5725-2:1994, 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
ISO 5725-3:1994, Accuracy (trueness and precision) of measurement methods and results — Part 3:
Intermediate measures of the precision of a standard measurement method
3 Principle
An inter laboratory test for method validation is organized at each stage of the development of a standard
draft. Changing economic conditions have led to the optimization of the work of the participating laboratories.
The principle retained by ECISS/TC 102 is to have three values by participant laboratory: two values obtained
in repeatability conditions (day 1) and a third obtained in intra laboratory reproducibility conditions (day 2). The
data evaluation requires a complex statistical analysis, which may be very confusing for a non-specialist, even
if it is widely detailed in the ISO 5725 standard. Consequently, it seems useful to clarify the methodology of
this standard for the above purpose and to underline that difficulties found should be discussed and solved
with statisticians.
Values that are identified as statistically abnormal at 99 % (outliers) using numerical Cochran’s and Grubbs’
tests lead to the elimination of the laboratory that produced them, at the stage at which they are detected: this
principle is adopted even though we risk wrongly eliminating one result in one hundred. Nevertheless, it is
essential to advise the laboratory concerned about the reasons for these eliminations and to pay particularly
attention to this laboratory's results.
Furthermore, in the case of a laboratory which produces values that are determined as statistically significant
at 95 % (stragglers) by numerical Cochran’s and Grubbs’ tests, particular attention should be paid to all the
other values produced by this laboratory.
4 Preliminary rules
4.1 First rule (‘to be clear’)
The inter laboratory test should be adapted in order to meet the following requirements:
— to estimate the variances linked to the tested method (repeatability, intra laboratory reproducibility, inter
laboratories reproducibility);
— to check that inter laboratories variance is compatible with defined criteria for referee or routine methods
(Aim CVR or Max CVR) within their full range of application.
The following shall be imposed on the working groups:
a) minimal number of participating laboratories (8 / 10 / 15… - see ISO 5725-1:1994, Annex B);
b) rigorous implementation of the working programme;
c) appropriate number of significant figures to be given for each transmitted value, in order to allow an
optimal statistical data evaluation.
4.2 Second rule (‘to be modest’)
The statistical treatment shall be performed by application of the ISO 5725 standard, and by following the
procedure described hereafter. In order to solve the statistical problems encountered, the help of an expert
should be sought. It should be noted that ISO 5725-2 and ISO 5725-3 don’t give an exhaustive description of
all situations and that they clearly indicate that statistical data treatment should be performed by a person
experienced in work planning and in statistical analysis (ISO 5725-2:1994, 6.2). Various situations may arise
in practice which require the application of the variance analysis general modes (ANOVA), and these
ISO 5725 standards only specify simplified procedures.
4.3 Minimal characteristics of data population
At least two samples should be tested for each concentration range to be determined, (for example between
0,010 and 0,099 we shall have two samples, between 0,10 and 0,99 we shall have two samples and so on),
and should never be less than 5 for the full range of values. It is useful, when possible, that the inter laboratory
test be performed using certified reference materials (CRMs) representing at least 50 % of the total number of
samples to be tested. The remaining samples can be internal reference materials provided by laboratories on
condition that their homogeneity has been tested and found to be compatible with inter laboratory test
requirements.
In the present economic situation, an inter laboratory test should be planned with at least 8 laboratories from
at least 5 different countries.
The values provided by the participating laboratories should have a sufficient number of significant figures in
order to enable correct statistical data treatment; although the number of significant figures does not influence
the precision of the result, the transmission of rounded values containing fewer figures means that the work
cannot be correctly evaluated. Expressed as a w/w percentage, values should generally be written under the
form listed below, i.e. containing 3 or 4 significant figures:
xx,xx
x,xxx
0,xxx x
0,0xx x
0,00x xx
0,000 xxx
5 Procedure
5.1 Bases
Here we look at the only case where the data population is strictly obtained by the methods defined in
Clause 3, that is to say, 3 determinations for each sample and from each laboratory:
— two determinations under repeatability conditions called ‘Day 1,1’ and ‘Day 1,2’;
— the third determination under reproducibility conditions called ‘Day 2’.
Statistical data evaluation is performed for each content level, that is to say in the present case, sample by
sample.
5.2 Raw data examination
Raw data shall be typed into a table and then printed. The raw data table should be studied in order to detect
potential typing errors in the data supplied by each participating laboratory and/or in the final input stage
(ISO 5725-2:1994, 7.2.6).
Performing a normality test of the data population to be tested is recommended.
5.3 Intra laboratory repeatability variance (Cochran’s test)
A first graphical evaluation of the raw data may be performed in order to test the intra laboratory repeatability
consistency by using Mandel’s k test (all data included): its only purpose is to get an overview of the data
population.
Further statistical treatments are carried out under the hypothesis that the intra laboratory repeatability
variances belong to the same normal population. Cochran’s test should therefore be performed
(ISO 5725-2:1994, 7.3.3) in order to detect unexpected values of intra laboratory variances, which shall then
be discarded so that statistical analysis may be pursued.
Strictly speaking, Cochran’s test should only be used to evaluate a population of measurements obtained in
repeatability conditions.
In practice, it is advisable to proceed as follows:
— perform Cochran’s test with ‘Day 1,1’ and ‘Day 1,2’ values, after a normality test for this data population;
— discard laboratories having an unexpected variance.
It is advisable not to perform an iteration when using Cochran’s test, except in the case of a large laboratory
population (i.e. greater than 15), or when there is a particular statistical reason to justify it. A common rule
sometimes used is that the outliers shall not represent more than 10 % of the whole data.
In practice, in order to have a clear view of the data after the Cochran’s test has been performed, it is
advisable either to print a new table of the remaining data or to clearly identify discarded data.
5.4 Intra laboratory reproducibility variance (Grubbs’ test)
Further statistical evaluations are carried out under the hypothesis that intermediate variances (intra
laboratory reproducibility) belong to the same normal population. Grubbs’ test should be applied
(ISO 5725-2:1994, 7.3.4) in order to detect unexpected means that should then be discarded so that statistical
analysis may be pursued.
In practice, it is advisable to proceed in the following order:
— apply Grubbs’ test to the ‘daily means’ data, that is to say to the pair of values ‘(Day 1,1 + Day 1,2)/2’ and
‘Day 2’ for all of the laboratories;
— firstly, test the highest ‘mean’ after having confirmed that the data population is normal;
— if the test is positive, discard the laboratory concerned;
— secondly, test the lowest ‘mean’;
— if the test is positive, discard the laboratory concerned;
— if neither of the two former tests detect an unexpected ‘mean’, perform the test with the two highest
‘mean’ values;
— if the test is positive discard the laboratory(ies) concerned;
— perform the test with the two lowest ‘
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