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1、BRITISH STANDARD BS ISO 16820:2004 Sensory analysis Methodology Sequential analysis ICS 67.240 ? Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 16820:2004 This British Standard was published under the authority of the Standards Polic
2、y and Strategy Committee on 1 July 2004 BSI 1 July 2004 ISBN 0 580 44006 0 National foreword This British Standard reproduces verbatim ISO 16820:2004 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee AW/12, Sensory analysis, w
3、hich has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitl
4、ed “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance
5、with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related inter
6、national and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii and iii, a blank page, pages 1 to 10, an inside back cover and a back cover. The BSI copyright notice displayed in this docume
7、nt indicates when the document was last issued. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Reference number ISO 16820:2004(E) OSI 4002 INTERNATIONAL STANDARD ISO 16820 First edit
8、ion 2004-06-15 Sensory analysis Methodology Sequential analysis Analyse sensorielle Mthodologie Analyse squentielle BS ISO 16820:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:02861 O4002(E) DPlcsid Fremia ihTs PDF file may ctnoian
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14、 (c) BSI IS:02861 O4002(E) I SO 4002 All irthgs ersedevr iii 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 commi
15、ttees. 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 I
16、nternational Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. 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 Internationa
17、l 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. Attention is drawn to the possibility that some of the elements of this document may be the
18、 subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 16820 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 12, Sensory analysis. BS ISO 16820:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10
19、GMT+00:00 2006, Uncontrolled Copy, (c) BSI blank BS ISO 16820:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontrolled Copy, (c) BSI INTENRATIONAL TSANDADR IS:02861 O4002(E) I SO 4002 All irthgs ersedevr 1 Sensory analysis Methodology Sequential analysis 1 Sc
20、ope This International Standard describes a procedure for statistically analysing data from forced-choice sensory discrimination tests, such as the Triangle, Duo-Trio, 3-AFC, 2-AFC, in which after every trial of the discrimination test the decision can be made to stop testing and declare a differenc
21、e, to stop testing and declare no difference, or to continue testing. The sequential method often allows for a decision to be made after fewer trials of the discrimination test than would be required by conventional approaches that use predetermined numbers of assessments. The method is effective fo
22、r a) determining that either a perceptible difference results, or a perceptible difference does not result when, for example, a change is made in ingredients, processing, packaging, handling or storage; b) or for selecting, training and monitoring assessors. 2 Normative references The following refe
23、renced 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 5492:1992, Sensory analysis Vocabulary 3 Terms, definitions and
24、 symbols 3.1 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 5492 and the following apply. 3.1.1 alpha-risk -risk probability of concluding that a perceptible difference exists when one does not NOTE This is also known as Type I error, significance lev
25、el or false positive rate. 3.1.2 beta-risk -risk probability of concluding that no perceptible difference exists when one does NOTE This is also known as Type II error or false negative rate. BS ISO 16820:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontroll
26、ed Copy, (c) BSI IS:02861 O4002(E) 2 I SO 4002 All irthgs ersedevr 3.1.3 sensitivity general term used to summarize the performance characteristics of the test NOTE In statistical terms, the sensitivity of the test is defined by the values of , and pd. 3.2 Symbols p0 probability of a correct respons
27、e when no perceptible difference exists pd proportion of assessments in which a perceptible difference is detected between the two products p1 probability of a correct response when a perceptible difference does exist 4 Principle The type of discrimination test (triangle, duo-trio, etc.) is chosen.
28、The sensitivity of the test is defined by selecting values for , and pd. The boundaries of the decision regions are computed based on , , p0 and p1. After every trial of the discrimination test, the total number of correct responses for the panel, see Clause 1a), or per assessor, see Clause 1b) is c
29、ompared to the decision boundaries to determine if testing can be stopped and a difference can be declared, if testing can be stopped and no difference can be declared, or if testing should continue. 5 Procedure 5.1 Construct a graph, as in Figure A.1, which illustrates the boundaries of the decisio
30、n regions based on , , p0 and p1 as follows. a) and are chosen based on the risks the researcher is willing to take of obtaining a false positive or a false negative result, respectively. is the probability of declaring that a difference exists when the true probability of a correct response is p0.
31、is the probability of failing to declare that a difference exists when the true probability of a correct response is p1 (p1 p0). b) p0 is the probability of a correct response when no perceptible difference exists (i.e. the probability of a correct guess). The value of p0 depends on the discriminati
32、on test being used: for the triangle and the 3-AFC tests, 0 1/3p= for the duo-trio and the 2-AFC tests, 0 1/2p= c) p1 is the probability of a correct response when a perceptible difference does exist. The value of p1 depends on pd: for the triangle and 3-AFC tests, d 1d 1 3 p pp =+ for the duo-trio
33、and 2-AFC tests, d 1d 1 2 p pp =+ BS ISO 16820:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:02861 O4002(E) I SO 4002 All irthgs ersedevr 3 d) the lines that form the boundaries of the decision regions are calculated as: lower line
34、: ( )()()() ()()()() 10 0 1010 lglg 1lg 1lg 1 lglglg 1lg 1 npnp d pppp + = + upper line: ()( )()() ()()()() 10 1 1010 lg 1lglg 1lg 1 lglglg 1lg 1 npnp d pppp + = + where , , p0 and p1 are as defined above, and n is the number of trials of the test. NOTE The distance between the two lines depends on
35、p1 p0. 5.2 After each trial of the discrimination test, plot the total number of correct responses (on the vertical axis) versus the number of trials (on the horizontal axis): if the total number of correct responses falls between the lower and upper lines on the chart, then continue testing by cond
36、ucting another trial; if the total number of correct responses falls above the upper line on the chart, then stop testing and conclude that a perceptible difference exists (at the -level of significance); if the total number of correct responses falls below the lower line on the chart, then stop tes
37、ting and conclude that no meaningful difference exists i.e. there is less than a (1 ) probability that the true probability of a correct response is as high as p1. BS ISO 16820:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:02861 O4
38、002(E) 4 I SO 4002 All irthgs ersedevr Annex A (informative) Examples A.1 Example 1 Sequential analysis of a series of triangle tests: acceptance vs. rejection of two trainees on a panel A.1.1 Background A sensory analyst wishes to base the decision to accept or reject two trainees on the panel on t
39、heir performance in triangle tests using a typical pair of products. Each trainee receives a series of triangle tests. Intervals between tests are kept long enough to avoid sensory fatigue. A.1.2 Test design The number of trials required to accept or reject a trainee is determined by sequential anal
40、ysis using a graph as shown in Figure A.1. To position the boundaries of the decision regions (i.e., the two lines in Figure A.1), assign a value to each of the four parameters, , , p0 and p1. In the triangle test 0 1/3p= (i.e. the probability of a correct guess, pd = 0). Usually the minimum accepta
41、ble rate of detection is set at pd = 50 %, which makes 1 12 0,50(10,50) ( ) 33 p=+= If it is desired to reduce the number of trials to reach a decision, lower the minimum acceptable rate of detection e.g. to pd = 40 %, which makes 1 1 0,40(10,40) ( )0,60 3 p=+=, etc. NOTE In this example the definit
42、ion of pd is not the proportion of the population of assessors who can distinguish the samples but rather the proportion of trials in which a single assessor actually distinguishes the samples. The analyst chooses the following values for the parameters: = 0,05 is the probability of selecting an una
43、cceptable trainee; = 0,10 is the probability of rejecting an acceptable trainee; 0 1/3p= is the maximum unacceptable ability (i.e. the null hypothesis p-value of the triangle test); 1 2/3p = is the minimum acceptable ability (i.e. the probability that the odd sample will be detected when pd = 0,50).
44、 BS ISO 16820:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:02861 O4002(E) I SO 4002 All irthgs ersedevr 5 A.1.3 Analysis and interpretation of results As each triangle is completed, the results are entered in the diagram in Figure
45、 A.1 as follows. Enter the result of the first trial, if correct, as (x, y) = (1,1) and, if incorrect, as (x, y) = (1,0). For each succeeding trial, increase the value of x by 1 and increase y by 1 for a correct response, or increase x by 1 and y by 0 for an incorrect response. Continue testing unti
46、l a plotted point touches or crosses either of the decision boundaries. Draw the indicated conclusion (i.e. accept or reject the trainee). Trainee A is correct in all tests and is accepted after five trials. Trainee B fails in the first triangle, succeeds in triangles 2 and 3, but then fails on ever
47、y subsequent triangle and is rejected after the 8th trial. = 0,05 = 0,10 Parameters of the test: p0 = 1 3 p1 = 2 3 10 0 1100 lg( )lg(1)lg(1)lg(1) Lower: lg()lg()lg(1)lg(1) npnp d pppp + = + 0 lg(0,10)lg(10,05)lg 1(2/3)lg 1(1/3) Lower: lg(2/3)lg(1/3)lg 1(2/3)lg 1(1/3) nn d + = + 0 Lower:1,6240,5dn= +
48、 Boundary lines: 10 1 1010 lg(1)lg( )lg(1)lg(1) Upper: lg()lg()lg(1)lg(1) npnp d pppp + = + 1 lg(10,10)lg(0,05)lg 1(2/3)lg 1(1/3) Upper: lg(2/3)lg(1/3)lg 1(2/3)lg 1(1/3) nn d + = + 1 Upper:2,0850,5dn=+ BS ISO 16820:2004 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 03:36:10 GMT+00:00 2006, Uncontrolled Copy, (c) BSI IS:02861 O4002(E) 6 I SO 4002 All irthgs ersedevr Key Trainee A Trainee B n is the number of trials d is the number of correct responses A is the acceptance region B is the continue testing region C is the rejection