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1、 Reference number ISO 16820:2004(E) ISO 2004 INTERNATIONAL STANDARD ISO 16820 First edition 2004-06-15 Sensory analysis Methodology Sequential analysis Analyse sensorielle Mthodologie Analyse squentielle Copyright International Organization for Standardization Provided by IHS under license with ISO
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7、mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2004 All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 00:54:04 MDTNo reproduction or netw
8、orking permitted without license from IHS -,-,- ISO 16820:2004(E) ISO 2004 All rights reserved 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 c
9、arried 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 that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the wor
10、k. ISO collaborates closely with the International 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 Inter
11、national Standards. Draft International 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 th
12、e 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 Technical Committee ISO/TC 34, Food products, Subcommittee SC 12, Sensory analysis. Copyright International Organization for Sta
13、ndardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 00:54:04 MDTNo reproduction or networking permitted without license from IHS -,-,- Copyright International Organization for Standardization Provided by IHS under license with
14、 ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 00:54:04 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISO 16820:2004(E) ISO 2004 All rights reserved 1 Sensory analysis Methodology Sequential analysis 1 Scope This Inte
15、rnational 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 difference, to stop te
16、sting 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 for a) determin
17、ing 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 referenced docume
18、nts 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 symbols 3.1
19、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 level or false p
20、ositive 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. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical S
21、tandards 1/9972545001 Not for Resale, 04/21/2007 00:54:04 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 16820:2004(E) 2 ISO 2004 All rights reserved 3.1.3 sensitivity general term used to summarize the performance characteristics of the test NOTE In statistical terms,
22、 the sensitivity of the test is defined by the values of , and pd. 3.2 Symbols p0 probability of a correct response 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 pe
23、rceptible 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 pd. The boundaries of the decision regions are computed based on , , p0 and p1. After every trial of the discriminati
24、on 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 declared, or if testing sho
25、uld continue. 5 Procedure 5.1 Construct a graph, as in Figure A.1, which illustrates the boundaries of the decision 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
26、. is the probability of declaring that a difference exists when the true probability of a correct response is p0. 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 pe
27、rceptible difference exists (i.e. the probability of a correct guess). The value of p0 depends on the discrimination 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 differen
28、ce 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 and 2-AFC tests, d 1d 1 2 p pp =+ Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for R
29、esale, 04/21/2007 00:54:04 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 16820:2004(E) ISO 2004 All rights reserved 3 d) the lines that form the boundaries of the decision regions are calculated as: lower line: ( )()()() ()()()() 10 0 1010 lglg 1lg 1lg 1 lglglg 1lg 1
30、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 p1 p0. 5.2 After each trial of the discrimination test, plo
31、t 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 conducting another trial; if the total number of correct respon
32、ses 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 testing and conclude that no meaningful difference exists i.e.
33、 there is less than a (1 ) probability that the true probability of a correct response is as high as p1. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 00:54:04 MDTNo reproducti
34、on or networking permitted without license from IHS -,-,- ISO 16820:2004(E) 4 ISO 2004 All rights reserved 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
35、base the decision to accept or reject two trainees on the panel on their 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 req
36、uired to accept or reject a trainee is determined by sequential analysis 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
37、probability of a correct guess, pd = 0). Usually the minimum acceptable 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
38、 1 0,40(10,40) ( )0,60 3 p=+=, etc. NOTE In this example the definition 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 valu
39、es for the parameters: = 0,05 is the probability of selecting an unacceptable 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. t
40、he probability that the odd sample will be detected when pd = 0,50). Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 00:54:04 MDTNo reproduction or networking permitted without l
41、icense from IHS -,-,- ISO 16820:2004(E) ISO 2004 All rights reserved 5 A.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
42、 (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 until a plotted point touches or crosses either of the decision boundaries. Draw the indicated conclusion (i.
43、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 every subsequent triangle and is rejected after the 8th trial. = 0,05 = 0,10 Parameters of the test: p0 = 1 3
44、 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= + 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
45、(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=+ Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 00:54:04 MDTNo reproduction or ne
46、tworking permitted without license from IHS -,-,- ISO 16820:2004(E) 6 ISO 2004 All rights reserved 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 region region NOTE At the 5th trial
47、, Trainee A passes out of the “continue testing region” and into the “acceptance region”. At the 8th trial, Trainee B passes out of the “continue testing region” and into the “rejection region”. Figure A.1 Use of sequential analysis in triangle tests Example 1: Selection of two trainees Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 00:54:04 MDTNo reproduction or networking permitted without li
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