CEN/TR 10345:2008
(Main)Guideline for statistical data treatment of inter laboratory tests for validation of analytical methods
Guideline for statistical data treatment of inter laboratory tests for validation of analytical methods
This document 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, -2 and -3:1994 standards for the treatment of registered data in the conditions used within the ECISS/TC 20 working groups.
NOTE The present document is not a simplification of ISO 5725 standard, which is the only reference document.
Richtlinien für statistische Verfahren der Probenahme und Analyse von Eisen, Stahl und anderen Eisenmetallen
Guide pour le traitement statistique des données de validation de méthodes d'analyse, issues d'essais interlaboratoire
Ce document est un guide pour le traitement statistique des données de validation de méthodes, issues
d'essais interlaboratoire.
Son but est de préciser dans le détail la méthodologie des normes ISO 5725-1, -2 et -3:1994 pour le
traitement de données obtenues dans les conditions mises en oeuvre au sein des groupes de travail de
l'ECISS/TC 20.
NOTE Le présent document n'est pas une simplification de la norme ISO 5725, qui est le seul document de
référence.
Smernice za statistične postopke vzorčenja in analize železa, jekla in drugih kovinskih materialov na osnovi železa
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2008
6PHUQLFH]DVWDWLVWLþQHSRVWRSNHY]RUþHQMDLQDQDOL]HåHOH]DMHNODLQGUXJLK
NRYLQVNLKPDWHULDORYQDRVQRYLåHOH]D
Guideline for statistical data treatment of inter laboratory tests for validation of analytical
methods
Richtlinien für statistische Verfahren der Probenahme und Analyse von Eisen, Stahl und
anderen Eisenmetallen
Guide pour le traitement statistique des données de validation de méthodes d'analyse,
issues d'essais interlaboratoire
Ta slovenski standard je istoveten z: CEN/TR 10345:2008
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
June 2008
ICS 03.120.30; 17.020
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 statistische Verfahren der Probenahme und
validation de méthodes d'analyse, issues d'essais Analyse von Eisen, Stahl und anderen Eisenmetallen
interlaboratoire
This Technical Report was approved by CEN on 22 October 2007. It has been drawn up by the Technical Committee ECISS/TC 20.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 10345:2008: E
worldwide for CEN national Members.
Contents Page
Foreword.3
1 Scope .4
2 Normative references .4
3 Principle.4
4 Preliminary rules.4
4.1 First rule (‘to be clear’) .4
4.2 Second rule (‘to be modest’) .5
4.3 Minimal characteristics of data population.5
5 Procedure .6
5.1 Bases .6
5.2 Raw data examination .6
5.3 Intra laboratory repeatability variance (Cochran’s test).6
5.4 Intra laboratory reproducibility variance (Grubbs’ test).6
5.5 Inter laboratory reproducibility variance (Grubbs’ test).7
5.6 Retained data examination .8
5.7 Calculation of the variances associated to the tested method.8
5.8 Treatment for unexpected calculated variances .8
5.9 Estimation of a function linking variance and level.8
6 Report .9
7 General remarks.9
Annex A Steps for the validation of a Draft Standard.10
Annex B Synoptic of the operations described in Annex A.12
Annex C Examples.17
Bibliography .46
Foreword
This document CEN/TR 10345:2008 has been prepared by Technical Committee ECISS/TC 20 “Methods of
chemical analysis of ferrous products”, the secretariat of which is held by SIS.
1 Scope
This document 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, -2 and -3:1994 standards for the treatment of
registered data in the conditions used within the ECISS/TC 20 working groups.
NOTE The present document is not a simplification of ISO 5725 standard, which is the only reference document
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 5725-1:1994, 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 organised at each stage of the development of a standard draft.
Changing economical conditions have lead to the optimisation of the work of the participating laboratories.
The principle retained by the ECISS/TC 20 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 5725:1994 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 to wrongly eliminating one result in one hundred. Nevertheless, it is
essential to investigate with the laboratory that produced the involved results the reasons for this elimination
and to pay particular attention to all of the values produced by this laboratory.
Also, 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 a 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) for their full range of application.
The following must be imposed on the working groups:
a) minimal number of participating laboratories (8 / 10 / 15… - see ISO 5725-1, 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 must be performed by application of the ISO 5725:1994 standard, and by following
the here after described procedure. In order to solve the statistical problems encountered, the help of an
expert should be sought. It should be noted that the ISO 5725-2 et 5725-3:1994 standards 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 § 6.2). Various
situations may arise in practice, which require the application of the variance analysis general modes
(ANOVA), these ISO 5725 standards specifying only simplified procedures.
4.3 Minimal characteristics of data population
The number of samples to be tested should be at least two for each range of values to be determined, (for
example between 0,010 and 0,099 we must have two samples, between 0,10 and 0,99 we must 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 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. These points are not the subject of the present document.
In the present economical situation, an inter laboratory test should be planed 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 less 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,xxxx
0,0xxx
0,00xxx
0,000xxx
5 Procedure
5.1 Bases
Here we look at the only case where the data population is strictly obtained by the methods defined in § 3, that
is to say, 3 determinations for each sample and from each laboratory:
two determinations in repeatability conditions called ‘Day 1,1’ et ‘Day 1,2’;
supplementary determination in 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 must 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 § 7.2.6).
NOTE 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 §
7.3.3) in order to detect unexpected values of intra laboratory variances, which must then be discarded so that
statistical analysis may be pursued.
NOTE 1 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;
if necessary, discard laboratories having an unexpected variance.
NOTE 2 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
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.