1、BSI Standards PublicationBS EN ISO 17994:2014Water quality Requirementsfor the comparison ofthe relative recovery ofmicroorganisms by twoquantitative methodsBS EN ISO 17994:2014 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of EN ISO17994:2014. It supersedes BS EN I
2、SO 17994:2004 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee EH/3/4, Microbiological methods.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessary
3、provisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2014. Published by BSI StandardsLimited 2014ISBN 978 0 580 73195 2ICS 07.100.20; 13.060.70Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standar
4、d was published under the authority of theStandards Policy and Strategy Committee on 28 February 2014.Amendments issued since publicationDate Text affectedEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 17994 February 2014 ICS 07.100.20; 13.060.70 Supersedes EN ISO 17994:2004English Version
5、 Water quality - Requirements for the comparison of the relative recovery of microorganisms by two quantitative methods (ISO 17994:2014) Qualit de leau - Exigences pour la comparaison du rendement relatif des microorganismes par deux mthodes quantitatives (ISO 17994:2014) Wasserbeschaffenheit - Anfo
6、rderungen fr den Vergleich der relativen Wiederfindung von Mikroorganismen durch zwei quantitative Verfahren (ISO 17994:2014) This European Standard was approved by CEN on 8 February 2014. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for gi
7、ving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member. This European Standard exists in three of
8、ficial versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CEN members are the national standards bodies
9、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
10、, Sweden, Switzerland, Turkey and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels 2014 CEN All rights of exploitation in any form and by any means reserved worldwide
11、for CEN national Members. Ref. No. EN ISO 17994:2014 EBS EN ISO 17994:2014EN ISO 17994:2014 (E) 3 Foreword This document (EN ISO 17994:2014) has been prepared by Technical Committee ISO/TC 147 “Water quality“ in collaboration with Technical Committee CEN/TC 230 “Water analysis” the secretariat of wh
12、ich is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by August 2014, and conflicting national standards shall be withdrawn at the latest by August 2014. Attention is drawn to the possi
13、bility 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 EN ISO 17994:2004. According to the CEN-CENELEC Internal Regulations, the national standards
14、 organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxemb
15、ourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. Endorsement notice The text of ISO 17994:2014 has been approved by CEN as EN ISO 17994:2014 without any modification. BS EN ISO 17994:2014ISO 17994:2014(E) ISO
16、2014 All rights reserved iiiContents PageForeword ivIntroduction v1 Scope . 12 Normative references 13 Terms, definitions and symbols 13.1 Terms and definitions . 13.2 Symbols and abbreviated terms. 34 Principle 35 Basic requirements for a comparison study 45.1 General . 45.2 Description of methods
17、. 45.3 Types of samples . 45.4 Number of samples and participating laboratories 55.5 Counting and confirming 76 Calculations 86.1 Preliminary editing of the raw data 86.2 Basic relative differences . 86.3 Half-width of the confidence interval 97 Evaluation 97.1 Preliminary evaluations 97.2 Two-sided
18、 evaluation . 107.3 One-sided evaluation 128 Test report 13Annex A (informative) Flowchart 14Annex B (informative) Comparison studies .15Annex C (informative) Derivation of equation for calculation of the number of samples .17Annex D (informative) Example of a two-sided evaluation 19Bibliography .22
19、BS EN ISO 17994:2014ISO 17994:2014(E)ForewordISO (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 i
20、nterested 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 Electrotechn
21、ical 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 do
22、cuments should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2, 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
23、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, www.iso.org/patents.Any trade name used in this document is information given for the conv
24、enience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword
25、 - Supplementary informationThe committee responsible for this document is ISO/TC 147, Water quality, Subcommittee SC 4, Microbiological methods.This second edition cancels and replaces the first edition (ISO 17994:2004), which has been technically revised.iv ISO 2014 All rights reservedBS EN ISO 17
26、994:2014ISO 17994:2014(E)IntroductionThis International Standard specifies criteria and procedures for comparing the average quantitative results obtained by two microbiological analytical methods, one of which may, but need not, be a standard or reference method.The methods considered are based on
27、counts of colonies or of positive and negative liquid enrichment tubes (MPN). ISO 2014 All rights reserved vBS EN ISO 17994:2014BS EN ISO 17994:2014Water quality Requirements for the comparison of the relative recovery of microorganisms by two quantitative methodsWARNING Persons using this document
28、should be familiar with normal laboratory practice. This document does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory c
29、onditions.IMPORTANT It is absolutely essential that tests conducted in accordance with this document be carried out by suitably qualified staff.1 ScopeThis International Standard specifies an evaluation procedure for comparing two methods with established performance characteristics according to ISO
30、/TR 13843 and intended for the quantification of the same target group or species of microorganisms.This International Standard provides the mathematical basis for the evaluation of the average relative performance of two quantitative methods against chosen criteria for the comparison. It does not p
31、rovide data for assessment of the precision of the methods being compared. It is appropriate that the precision of methods is assessed as part of their performance characterization.This International Standard does not provide methods for the verification of method performance characterization in a s
32、ingle laboratory.2 Normative referencesThe 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 (inc
33、luding any amendments) applies.ISO 8199, Water quality General guidance on the enumeration of micro-organisms by cultureISO/TR 13843, Water quality Guidance on validation of microbiological methods3 Terms, definitions and symbols3.1 Terms and definitionsFor the purposes of this document, the followi
34、ng terms and definitions apply.3.1.1 General terms3.1.1.1comparison trialinterlaboratory method comparison that involves laboratories which perform paired measurements on several of their own samples with two different methodsINTERNATIONAL STANDARD ISO 17994:2014(E) ISO 2014 All rights reserved 1BS
35、EN ISO 17994:2014ISO 17994:2014(E)3.1.1.2not-different methodmethod considered quantitatively not different to another method when the mean difference between their confirmed counts and stipulated difference lie between predetermined stipulated limits, taking into account all sources of variationNot
36、e 1 to entry: This difference can be assessed by the average relative difference of their confirmed counts.3.1.1.3predetermined stipulated limitpermitted average difference (based on a “confidence interval” designated 2L to +2L) between results obtained by each method, based on professional practice
37、s or regulatory requirementsNote 1 to entry: Reference 1 suggests that, in international and interlaboratory method performance tests, a limit of 2L = 10 % for setting the “confidence interval” be the predetermined stipulated limit for drinking water, and this has been widely used. However, for envi
38、ronmental waters, such as bathing waters, Reference 2 proposes a predetermined stipulated limit of 2L = 20 %.3.1.1.4reference methodmethod of analysis internationally recognized by experts or by agreement between the partiesNote 1 to entry: As a rule, the reference method is a standard or a commonly
39、 used method.3.1.1.5standard measurement uncertaintymeasurement uncertainty expressed as a standard deviationSOURCE: ISO/IEC Guide 99:2007 (3), 2.303.1.1.6trial methodany method which is to be tested for comparison with a reference method3.1.2 Specific terms3.1.2.1countobserved number of objectsEXAM
40、PLE Colonies or cells of microorganisms, plaques of bacteriophagesNote 1 to entry: In this International Standard, the result of an MPN estimation is also considered to be a count.3.1.2.2presumptive countcolony count or most probable number (MPN) estimate based on the number of colonies or fermentat
41、ion tubes that have an outward appearance that is interpreted as typical of a target organism3.1.2.3confirmed countpresumptive count multiplied by the confirmation coefficient3.1.2.4relative differenceRDdifference between two results, a and b, measured on a relative (natural logarithmic) scale2 ISO
42、2014 All rights reservedBS EN ISO 17994:2014ISO 17994:2014(E)3.2 Symbols and abbreviated termsA (symbol for the idea of) trial methoda test result by method Aaitest result (confirmed count) of method A in sample iB (symbol for the idea of) reference methodb test result by method Bbitest result (conf
43、irmed count) of method B in sample ii subscript indicating a seriesk coverage factor used for calculating the confidence intervalL smallest microbiologically significant mean relative difference between the results by methods A and BMPN most probable number quantitative methodn number of sampless ex
44、perimental standard deviation of the relative difference (standard uncertainty)s2experimental variancesxstandard deviation of the relative difference (standard uncertainty) of the meanW half-width of the confidence intervalx relative differencexivalue of the relative difference between aiand biin sa
45、mple ixarithmetic mean of xi(i = 1,2 n)xLvalue of the relative difference at the lower confidence limit, derived by subtracting the value of the half-width of the confidence interval from the meanxUvalue of the relative difference at the upper confidence limit, derived by adding the value of the hal
46、f-width of the confidence interval to the meanX2experimental Poisson index of dispersiony conditional variable used in computing the number of samples for comparison testing4 PrincipleThis International Standard is based on the principle of the paired t-test (see Annex C).The basic data are pairs of
47、 confirmed counts (ai, bi) obtained from the examination of two equal portions taken from the same vessel of a carefully mixed test sample, one determination (count) per method. The complete design consists of a large number of similar determinations.In this International Standard, two methods are c
48、onsidered quantitatively “not different” if the mean relative difference of the paired confirmed counts does not differ significantly from zero and the ISO 2014 All rights reserved 3BS EN ISO 17994:2014ISO 17994:2014(E)confidence interval does not extend beyond the level of the predetermined stipula
49、ted limit. The decision rules based on the above principle are given in 7.2 and 7.3 and a flow chart is given in Annex A.5 Basic requirements for a comparison study5.1 GeneralBoth methods shall have data on detailed performance characteristics, derived in accordance with the guidance outlined in ISO/TR 13843.The most important basic requirement of comparison studies is a wide range of samples. Participation by a number of laboratories is preferable, allowing the expansion of the sample range over large geographical areas. Also the credi
