1、Designation: E 2164 01Standard Test Method forDirectional Difference Test1This standard is issued under the fixed designation E 2164; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parenthese
2、s indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This Test Method covers a procedure for comparing twoproducts using a two-alternative forced-choice task.1.2 This method is sometimes referred to as a pai
3、redcomparison test or as a 2-AFC (alternative forced choice) test.1.3 A directional difference test determines whether a dif-ference exists in the perceived intensity of a specified sensoryattribute between two samples.1.4 Directional difference testing is limited in its applicationto a specified se
4、nsory attribute and does not directly determinethe magnitude of the difference for that specific attribute.Assessors must be able to recognize and understand thespecified attribute.Alack of difference in the specified attributedoes not imply that no overall difference exists.1.5 This test method doe
5、s not address preference.1.6 A directional difference test is a simple task for asses-sors, and is used when sensory fatigue or carryover is aconcern. The directional difference test does not exhibit thesame level of fatigue, carryover, or adaptation as multiplesample tests such as triangle or duo-t
6、rio tests. For detail oncomparisons among the various difference tests, see referen-cess. (1), (2), and (3).21.7 The procedure of the test described in this documentconsists of presenting a single pair of samples to the assessors.1.8 This standard does not purport to address all of thesafety concern
7、s, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 253 Terminology Relating to Sensory Evalu
8、ation of Ma-terials and Products3E 456 Terminology Relating to Quality and Statistics4E 1871 Practice for Serving Protocol for Sensory Evalua-tion of Foods and Beverages32.2 ASTM Publications:Manual 26 Sensory Testing Methods, 2nd EditionSTP 758 Guidelines for the Selection and Training ofSensory Pa
9、nel MembersSTP 913 Guidelines. Physical Requirements for SensoryEvaluation Laboratories2.3 ISO Standard:ISO 5495 Sensory AnalysisMethodologyPaired Com-parison3. Terminology3.1 For definition of terms relating to sensory analysis, seeTerminology E 253, and for terms relating to statistics, seeTermino
10、logy E 456.3.2 Definitions of Terms Specific to This Standard:3.2.1 a (alpha) riskthe probability of concluding that aperceptible difference exists when, in reality, one does not (alsoknown as type I error or significance level).3.2.2 b (beta) riskthe probability of concluding that noperceptible dif
11、ference exists when, in reality, one does (alsoknown as type II error).3.2.3 one-sided testa test in which the researcher has an apriori expectation concerning the direction of the difference. Inthis case, the alternative hypothesis will express that theperceived intensity of the specified sensory a
12、ttribute is greater(that is, AB) (or lower (that is, A 65 % represents “large” values.8.3 Having defined the required sensitivity for the test using8.2, use Table 1 or Table 2 to determine the number ofassessors necessary. Enter the table in the section correspond-ing to the selected value of Pmaxan
13、d the column correspondingto the selected value of b. The minimum required number ofassessors is found in the row corresponding to the selectedvalue of a. Alternatively, Table 1 or Table 2 can be used todevelop a set of values for Pmax, a, and b that provideacceptable sensitivity while maintaining t
14、he number of asses-sors within practical limits.8.4 Often in practice, the number of assessors is determinedby material conditions (e.g., duration of the experiment,number of available assessors, quantity of sample). However,increasing the number of assessors increases the likelihood ofTABLE 1 Numbe
15、r of Assessors Needed for a Directional Difference Test One-Sided Alternativeba 0.50 0.40 0.30 0.20 0.10 0.05 0.01 0.0010.50 Pmax=75 % 2 4 4 4 8 12 20 340.40 2 4 4 6 10 14 28 420.3 6 810142030480.20 6 6 10 12 20 26 40 580.10 10 10 14 20 26 34 48 700.5 14161824344258820.01 22 28 34 40 50 60 80 1080.0
16、01 38 44 52 62 72 84 108 1400.50 Pmax=70%4 4 4 8121832600.40 4 4 6 8 14 26 42 700.30 6 8 10 14 22 28 50 780.2 101220304060940.10 14 20 22 28 40 54 80 1140.05 18 24 30 38 54 68 94 1320.01 36 42 52 64 80 96 130 1740.001 62 72 82 96 118 136 176 2280.50 Pmax=65 % 4 4 4 8 18 32 62 1020.40 4 6 8 14 30 42
17、76 1200.3 8101424405488140.20 10 18 22 32 50 68 110 1660.10 22 28 38 54 72 96 146 2080.05 30 42 54 70 94 120 174 2440.01 64 78 90 112 144 174 236 3200.001 108 126 144 172 210 246 318 4120.50 Pmax=60 % 4 4 8 18 42 68 134 2380.40 6 10 24 36 60 94 172 2820.30 12 22 30 50 84 120 206 3280.20 22 32 50 78
18、112 158 254 3840.10 46 66 86 116 168 214 322 4720.05 72 94 120 158 214 268 392 5540.01 142 168 208 252 326 392 536 7260.001 242 282 328 386 480 556 732 9440.50 Pmax=55 % 4 8 28 74 164 272 542 9520.40 10 36 62 124 238 362 672 11240.30 30 72 118 200 334 480 810 13020.20 82 130 194 294 452 618 1006 155
19、60.10 170 240 338 462 658 862 1310 19060.05 282 370 476 620 866 1092 1584 22380.01 550 666 820 1008 1302 1582 2170 29280.001 962 1126 1310 1552 1908 2248 2938 3812NOTEThe values recorded in this table have been rounded to the nearest whole number evenly divisible by two to allow for equal presentati
20、on ofboth pair combinations (AB and BA).E2164013detecting small differences. Thus, one should expect to uselarger numbers of assessors when trying to demonstrate thatsamples are similar compared to when one is trying to showthey are different.9. Procedure9.1 Prepare serving order worksheet and ballo
21、t in advanceof the test to ensure a balanced order of sample presentation ofthe two samples, A and B. Balance the serving sequences ABand BA across all assessors. Serving order worksheets shouldalso include complete sample identification information. SeeExample Appendix X1.9.2 It is critical to the
22、validity of the test that assessorscannot identify the samples from the way in which they arepresented. For example, in a test evaluating flavor differences,one should avoid any subtle differences in temperature orappearance caused by factors such as the time sequence ofpreparation. It may be possib
23、le to mask color differences usinglight filters, subdued illumination or colored vessels. Code thevessels containing the samples in a uniform manner using3-digit numbers chosen at random for each test. Preparesamples out of sight and in an identical manner: sameapparatus, same vessels, same quantiti
24、es of sample (see Prac-tice E 1871-91).9.3 Present each pair of samples simultaneously wheneverpossible, following the same spatial arrangement for eachassessor (on a line to be sampled always from left to right, orfrom front to back, etc.). Within the pair, assessors are typicallyallowed to make re
25、peated evaluations of each sample asdesired. If the conditions of the test require the prevention ofrepeat evaluations, for example, if samples are bulky, leave anaftertaste, or show slight differences in appearance that cannotbe masked, present the samples monadically (or sequentialmonadic) and do
26、not allow repeated evaluations.9.4 Ask only one question about the samples. The selectionthe assessor has made on the initial question may bias the replyto subsequent questions about the samples. Responses toadditional questions may be obtained through separate tests forpreference, acceptance, degre
27、e of difference, etc See Manual26. A section soliciting comments may be included followingthe initial forced-choice question.TABLE 2 Number of Assessors Needed for a Directional Difference Test Two-Sided Alternativeba 0.50 0.40 0.30 0.20 0.10 0.05 0.01 0.0010.50 Pmax=75 % 2 6 8 12 16 24 34 520.40 6
28、6 10 12 20 26 40 580.30 6 8 12 16 22 30 42 640.20 10 10 14 20 26 34 48 700.10 14 16 18 24 34 42 58 820.05 18 20 26 30 42 50 68 920.01 26 34 40 44 58 66 88 1180.001 42 50 58 66 78 90 118 1500.50 Pmax=70% 6 81216263454860.4 6101220304060943 81418223444681020.20 14 20 22 28 40 54 80 1140.10 18 24 30 38
29、 54 68 94 1320.05 26 36 40 50 66 80 110 1500.01 44 50 60 74 92 108 144 1920.001 68 78 90 102 126 148 188 2400.50 Pmax=65 % 8 14 18 30 44 64 98 1560.40 10 18 22 32 50 68 110 1660.30 14 20 30 42 60 82 126 1880.20 22 28 38 54 72 96 146 2080.10 30 42 54 70 94 120 174 2440.05 44 56 68 90 114 146 200 2760
30、.01 74 92 108 132 164 196 262 3460.001 122 140 162 188 230 268 342 4400.50 Pmax=60 % 16 28 36 64 98 136 230 3520.40 22 32 50 78 112 158 254 3840.30 32 44 66 90 134 180 284 4260.20 46 66 86 116 168 214 322 4720.10 72 120 158 214 268 392 5540.05 102 126 158 200 264 328 456 6360.01 172 204 242 292 374
31、446 596 7960.001 276 318 364 426 520 604 782 10100.50 Pmax=55 % 50 96 156 240 394 544 910 14240.40 82 130 194 294 452 618 1006 15560.30 110 174 254 360 550 722 1130 17020.20 170 240 338 462 658 862 1310 19060.10 282 370 476 620 866 1092 1584 22380.05 390 498 620 786 1056 1302 1834 25440.01 670 802 9
32、64 1168 1494 1782 2408 32040.001 1090 1260 1462 1708 2094 2440 3152 4064NOTEThe values recorded in this table have been rounded to the nearest whole number evenly divisible by two to allow for equal presentation ofboth pair combinations (AB and BA).E21640149.5 The directional difference test is a fo
33、rced-choice proce-dure; assessors are not allowed the option of reporting “nodifference.” An assessor who detects no difference between thesamples should be instructed to make a guess and select one ofthe samples, and can indicate in the comments section that theselection was only a guess.10. Analys
34、is and Interpretation of Results10.1 The procedure used to analyze the results of a direc-tional difference test depends on the number of assessors.10.1.1 If the number of assessors is equal to or greater thanthe value given in Table 1 (for a one-sided alternative) or Table2 (for a two-sided alterna
35、tive) for the chosen values of a, b,and Pmax, then use Table 3 to analyze the data obtained from aone-sided test and Table 4 to analyze the data from a two-sidedtest. If the number of common responses is equal to or greaterthan the number given in the table, conclude that a perceptibleattribute diff
36、erence exists between the samples. If the numberof common responses is less than the number given in thetable, conclude that the samples are similar in attribute inten-sity and that no more than Pmaxof the population wouldperceive the difference at a confidence level equal to 1-b.Again, the conclusi
37、ons are based on the risks accepted whenthe sensitivity (that is, Pmax, a, and b) was selected indetermining the number of assessors.10.1.2 If the number of assessors is less than the value givenin Table 1 or Table 2 for the chosen values of a, b, and Pmaxand the researcher is primarily interested i
38、n testing for adifference, then use Table 3 to analyze the data obtained froma one-sided test or Table 4 to analyze the data obtained from atwo-sided test. If the number of common responses is equal toor greater than the number given in the table, conclude that aperceptible attribute difference exis
39、ts between the samples atthe a-level of significance.10.1.3 If the number of assessors is less than the value givenin Table 1 or Table 2 for the chosen values of a, b, and Pmaxand the researcher is primarily interested in testing for simi-larity, then a one-sided confidence interval is used to analy
40、zethe data obtained from the test. The calculations are as follows:Pc5 c/nScstandard error of Pc! 5 =Pc1Pc! / nconfidence limit 5 Pc1 zbScwhere:zb= the one-sided critical value of the standard normaldistribution, andc = the number of common responses.Values of zbfor some commonly used values of b-ri
41、sk are:b-risk zb0.50 0.0000.40 0.2530.30 0.5240.20 0.8420.10 1.2820.05 1.6450.01 2.3260.001 3.090If the confidence limit is less than Pmax, then conclude thatthe samples are similar in attribute intensity (that is, no morethan Pmaxof the population would perceive a difference at theTABLE 3 Number of
42、 Selected Responses Needed ForSignificance in a Directional Difference Test, One-SidedAlternativeNOTEEntries are the minimum number of common responses requiredfor significance at the stated significance level (column) for the corre-sponding number of assessors n (row). Reject the assumption of “nod
43、ifference” if the number of correct responses is greater than or equal tothe tabled value.Significance level (%)n .50 .20 .10 .05 .01 .0014 3 4 4 . . .5 4 4 5 5 . .6 4 5 6 6 . .746677.856778967789.1067891010689912 7 8 9 10 11 1213 7 9 10 10 12 1314 8 10 10 11 12 1315 91 11213 416 9 11 12 12 14 1517
44、9 11 12 13 14 1618 10 12 13 13 15 1619 10 12 13 14 15 1720 11 13 14 15 16 1821 12 13 14 15 17 1822 12 14 15 16 17 1923 12 15 16 16 18 2024 13 15 16 17 19 2025 13 16 17 18 19 2126 14 16 17 18 20 2227 14 17 18 19 20 2228 15 17 18 19 21 2329 16 18 19 20 22 2430 16 18 20 20 22 2431 16 19 20 21 23 2532 1
45、7 19 21 22 24 2633 17 20 21 22 24 2634 18 20 22 23 25 2735 19 21 22 23 25 2736 19 22 23 24 26 2840 21 24 25 26 28 3144 23 26 27 28 31 3348 25 28 29 31 33 3652 27 30 32 33 35 3856 29 32 34 35 38 4060 31 34 36 37 40 4364 33 36 38 40 42 4568 35 38 40 42 45 4872 37 41 42 44 47 5076 39 43 45 46 49 5280 4
46、1 45 47 48 51 5584 43 47 49 51 54 5788 45 49 51 53 56 5992 47 51 53 55 58 6296 49 53 55 57 60 64100 51 55 57 59 63 66NOTE 1For values of n not in the table, compute the missing entry asfollows: Minimum number of responses (x) = nearest whole numbergreater thanx=(n/2) + z =n/4 , where z varies with t
47、he significance levelas follows: 0.84 for a=0.20; 1.28 for a = 0.10; 1.64 for a = 0.05; 2.33 fora = 0.01; 3.10 for a = 0.001. This calculation is an approximation. Thevalue obtained may differ from the exact value as presented in the table,but the difference never exceeds one response. Exact values
48、can beobtained from binomial distribution functions widely available in statis-tical computer packages.NOTE 2Adapted from Meilgaard, M., Civille, G.V., and Carr, B.T.Sensory Evaluation Techniques, 2nd Edition. CRC Press, Inc., BocaRaton, FL, 1991, p. 339.E2164015b-level of significance). If the conf
49、idence limit is greater thanPmax, then similarity has not been demonstrated.10.2 If desired, calculate a two-sided confidence interval onthe proportion of common responses. The method is describedin Example X4.11. Report11.1 Report the test objective, the results, and the conclu-sions. The following additional information is highly recom-mended:11.1.1 The purpose of the test and the nature of thetreatment studied;11.1.2 Full identification of the samples: origin, method ofpreparation, quantity, shape, storage prior to testing, servingsize, and temperature. (Sample information
