1、BRITISH STANDARD BS ISO 16820:2004 Sensory analysis Methodology Sequential analysis ICS 67.240 BS ISO 16820:2004 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 1 July 2004 BSI 1 July 2004 ISBN 0 580 44006 0 National foreword This British Sta
2、ndard 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, which has the responsibility to: A list of organizations represented on this committee can be obtained on requ
3、est 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 entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Ca
4、talogue 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 with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understan
5、d 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 international and European developments and promulgate them in the UK. Summary of pages This document comprises a
6、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 document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments Re
7、ference number ISO 16820:2004(E) OSI 4002INTERNATIONAL STANDARD ISO 16820 First edition 2004-06-15 Sensory analysis Methodology Sequential analysis Analyse sensorielle Mthodologie Analyse squentielle BSISO16820:2004IS:02861 O4002(E) DPlcsid Fremia ihTs PDF file may ctnoian emdebt dedyfepcaes. In cca
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12、21-HC 02 av leT. 4 + 10 947 22 1 11 xaF0 947 22 14 + 9 74 E-mail coirypthgiso.o gr We bwww.is.o gro Pulbisdehi n Switlrez dnaii ISO 4002 Allr ithgsr esedevrBSISO16820:2004IS:02861 O4002(E) I SO 4002 All irthgs ersedevr iiiForeword ISO (the International Organization for Standardization) is a worldwi
13、de 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 tha
14、t committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in a
15、ccordance 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 re
16、quires 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 subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 16820 was prepared by Techn
17、ical Committee ISO/TC 34, Food products, Subcommittee SC 12, Sensory analysis. BSISO16820:2004blank BSISO16820:2004INTENRATIONAL TSANDADR IS:02861 O4002(E)I SO 4002 All irthgs ersedevr 1Sensory analysis Methodology Sequential analysis 1 Scope This International Standard describes a procedure for sta
18、tistically 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 difference, to stop testing and declare no difference, or to continue
19、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 for a) determining that either a perceptible difference results
20、, 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 referenced documents are indispensable for the application of thi
21、s 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 symbols 3.1 Terms and definitions For the purposes of this d
22、ocument, 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 level or false positive rate. 3.1.2 beta-risk -risk probability
23、of concluding that no perceptible difference exists when one does NOTE This is also known as Type II error or false negative rate. BSISO16820:2004IS:02861 O4002(E) 2 I SO 4002 All irthgs ersedevr3.1.3 sensitivity general term used to summarize the performance characteristics of the test NOTE In stat
24、istical terms, the sensitivity of the test is defined by the values of , and p d . 3.2 Symbols p 0 probability of a correct response when no perceptible difference exists p d proportion of assessments in which a perceptible difference is detected between the two products p 1 probability of a correct
25、 response when a perceptible difference does exist 4 Principle The type of discrimination test (triangle, duo-trio, etc.) is chosen. The sensitivity of the test is defined by selecting values for , and p d . The boundaries of the decision regions are computed based on , , p 0and p 1 . After every tr
26、ial of the discrimination test, the total number of correct responses for the panel, see Clause 1a), or per assessor, see Clause 1b) is compared 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 decl
27、ared, or if testing should continue. 5 Procedure 5.1 Construct a graph, as in Figure A.1, which illustrates the boundaries of the decision regions based on , , p 0and p 1as follows. a) and are chosen based on the risks the researcher is willing to take of obtaining a false positive or a false negati
28、ve result, respectively. is the probability of declaring that a difference exists when the true probability of a correct response is p 0 . is the probability of failing to declare that a difference exists when the true probability of a correct response is p 1(p 1 p 0 ). b) p 0is the probability of a
29、 correct response when no perceptible difference exists (i.e. the probability of a correct guess). The value of p 0depends on the discrimination test being used: for the triangle and the 3-AFC tests, 0 1/ 3 p = for the duo-trio and the 2-AFC tests, 0 1/ 2 p = c) p 1is the probability of a correct re
30、sponse when a perceptible difference does exist. The value of p 1depends on p d : for the triangle and 3-AFC tests, d 1d 1 3 p pp =+ for the duo-trio and 2-AFC tests, d 1d 1 2 p pp =+ BSISO16820:2004IS:02861 O4002(E) I SO 4002 All irthgs ersedevr 3d) the lines that form the boundaries of the decisio
31、n regions are calculated as: lower line: ( ) ( ) ( ) ( ) ()()( )( ) 10 0 1010 lg lg 1 lg 1 lg 1 lg lg lg 1 lg 1 npnp d pppp + = +upper line: ( ) ( ) ( ) ( ) ()()( )( ) 10 1 1010 lg 1 lg lg 1 lg 1 lg lg lg 1 lg 1 npnp d pppp + = +where , , p 0and p 1are as defined above, and n is the number of trials
32、 of the test. NOTE The distance between the two lines depends on p 1 p 0 . 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 t
33、he lower and upper lines on the chart, then continue testing by conducting 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 corr
34、ect responses falls below the lower line on the chart, then stop testing 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 p 1 . BSISO16820:2004IS:02861 O4002(E) 4 I SO 4002 All irthgs ersedevrAn
35、nex 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 their performance in triangle tests using
36、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 analysis using a graph as shown in Figure A.1
37、. 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, , , p 0and p 1 . In the triangle test 0 1/ 3 p = (i.e. the probability of a correct guess, p d= 0). Usually the minimum acceptable rate of detection is set at p d=
38、 50 %, which makes 1 12 0,50 (1 0,50) ( ) 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 p d= 40 %, which makes 1 1 0,40 (1 0,40) ( ) 0,60 3 p=+ =, etc. NOTE In this example the definition of p dis not the proporti
39、on 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 unacceptable trainee; = 0,10 is
40、the probability of rejecting an acceptable trainee; 0 1/ 3 p = is the maximum unacceptable ability (i.e. the null hypothesis p-value of the triangle test); 1 2/3 p = is the minimum acceptable ability (i.e. the probability that the odd sample will be detected when p d= 0,50). BSISO16820:2004IS:02861
41、O4002(E) I SO 4002 All irthgs ersedevr 5A.1.3 Analysis and interpretation of results As each triangle is completed, the results are entered in the diagram in Figure 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 succe
42、eding 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 until a plotted point touches or crosses either of the decision boundaries. Draw the indicated conclusion (i.e. accept or reject the trainee
43、). 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 every subsequent triangle and is rejected after the 8 thtrial. = 0,05 = 0,10 Parameters of the test: p 0= 1 3p 1= 2 310 0 110 0 lg( ) lg(1 )
44、 lg(1 ) lg(1 ) Lower: lg( ) lg( ) lg(1 ) lg(1 ) npnp d pp pp + = +0 lg(0,10) lg(1 0,05) 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: 1,624 0,5 dn = + Boundary lines: 10 1 10 10 lg(1 ) lg( ) lg(1 ) lg(1 ) Upper: lg( ) lg( ) lg(1 ) lg(1 ) npnp d pp pp + = +1 l
45、g(1 0,10) 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: 2,085 0,5 dn =+ BSISO16820:2004IS:02861 O4002(E) 6 I SO 4002 All irthgs ersedevrKey Trainee A Trainee B n is the number of trials d is the number of correct responses A is the acceptance region
46、B is the continue testing region C is the rejection region region NOTE At the 5 thtrial, Trainee A passes out of the “continue testing region” and into the “acceptance region”. At the 8 thtrial, Trainee B passes out of the “continue testing region” and into the “rejection region”. Figure A.1 Use of
47、sequential analysis in triangle tests Example 1: Selection of two trainees BSISO16820:2004IS:02861 O4002(E) I SO 4002 All irthgs ersedevr 7A.2 Example 2 Sequential analysis of a series of duo-trio tests: Warmed-over flavour (WOF) in beef patties during storage A.2.1 Background A manufacturers qualit
48、y control panel has detected warmed-over flavour (WOF) in beef patties refrigerated for 5 days and then reheated. The project leader wants to set a reasonable maximum for the number of days the beef patties may be refrigerated. A.2.2 Test design Preliminary evaluations have shown that beef patties stored for 5 days exhibit strong WOF while patties stored for 1 day exhibit no WOF. The sensory analyst chooses to run a series of duo-trio tests involving patties that have been stored for 1, 3 and 5
