1、Designation: E 2164 08Standard 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 Ennis (1),MacRae (2), and OMahony and Odbert (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
7、thesafety concerns, 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:3E 253 Terminology Relatin
8、g to Sensory Evaluation of Ma-terials and ProductsE 456 Terminology Relating to Quality and StatisticsE 1871 Guide for Serving Protocol for Sensory Evaluationof Foods and Beverages2.2 ISO Standard:ISO 5495 Sensory AnalysisMethodologyPaired Com-parison3. Terminology3.1 For definition of terms relatin
9、g to sensory analysis, seeTerminology E 253, and for terms relating to statistics, seeTerminology 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 o
10、r significance level).3.2.2 b (beta) riskthe probability of concluding that noperceptible difference 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, t
11、he alternative hypothesis will express that theperceived intensity of the specified sensory attribute 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 ofasses
12、sors necessary. Enter the table in the section correspond-ing to the selected value of Pmaxand 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 todeve
13、lop a set of values for Pmax, a, and b that provideacceptable sensitivity while maintaining the 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
14、 sample). However,TABLE 1 Number of Assessors Needed for a Directional Difference Test One-Sided AlternativeNOTE 1The 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).NOTE 2Adapted
15、 from Meilgaard et al (8).ba 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 1080.001 38 44 52 62 72 84 108 1400.50 Pmax=70%4 4 4 8121
16、832600.40 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 76 1200.3 8101424405488140.20 10 18 22 32 50 68 110
17、 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 78 112 158 254 3840.10 46 66 86 116 168 214 322 4720.0
18、5 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 15560.10 170 240 338 462 658 862 1310 19060.05 282 370
19、 476 620 866 1092 1584 22380.01 550 666 820 1008 1302 1582 2170 29280.001 962 1126 1310 1552 1908 2248 2938 3812E2164083increasing the number of assessors increases the likelihood ofdetecting small differences. Thus, one should expect to uselarger numbers of assessors when trying to demonstrate that
20、samples are similar compared to when one is trying to showthey are different.9. Procedure9.1 Prepare serving order worksheet and ballot 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. Ser
21、ving order worksheets shouldalso include complete sample identification information. SeeAppendix X1.9.2 It is critical to the 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
22、any subtle differences in temperature orappearance caused by factors such as the time sequence ofpreparation. It may be possible to mask color differences usinglight filters, subdued illumination or colored vessels. Code thevessels containing the samples in a uniform manner using3-digit numbers chos
23、en at random for each test. Preparesamples out of sight and in an identical manner: sameapparatus, same vessels, same quantities of sample (see GuideE 1871-91).9.3 Present each pair of samples simultaneously wheneverpossible, following the same spatial arrangement for eachassessor (on a line to be s
24、ampled always from left to right, orfrom front to back, etc.). Within the pair, assessors are typicallyallowed to make repeated 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 s
25、how slight differences in appearance that cannotbe masked, present the samples monadically (or sequentialmonadic) and do 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 ab
26、out the samples. Responses toadditional questions may be obtained through separate tests forTABLE 2 Number of Assessors Needed for a Directional Difference Test Two-Sided AlternativeNOTE 1The values recorded in this table have been rounded to the nearest whole number evenly divisible by two to allow
27、 for equal presentation ofboth pair combinations (AB and BA).NOTE 2Adapted from Meilgaard et al (8).ba 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 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
28、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 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 Pm
29、ax=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 2760.01 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
30、 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 6360.01 172 204 242 292 374 446 596 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 4
31、52 618 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 25440.01 670 802 964 1168 1494 1782 2408 32040.001 1090 1260 1462 1708 2094 2440 3152 4064E2164084preference, acceptance, degree of d
32、ifference, etc. See Cham-bers and Baker Wolf (9).Asection soliciting comments may beincluded following the initial forced-choice question.9.5 The directional difference test is a forced-choice proce-dure; assessors are not allowed the option of reporting “nodifference.” An assessor who detects no di
33、fference 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. Analysis and Interpretation of Results10.1 The procedure used to analyze the results of a direc-tional difference test depend
34、s 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 alternative) for the chosen values of a, b,and Pmax, then use Table 3 to analyze the data obtained from aone-sided test and Ta
35、ble 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 difference exists between the samples. If the numberof common responses is less than the number given in thetable, conclude
36、 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 conclusions are based on the risks accepted whenthe sensitivity (that is, Pmax, a, and b) was selected indetermining the number
37、 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 in testing for adifference, then use Table 3 to analyze the data obtained froma one-sided test or Table 4 to analyze the
38、 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 exists between the samples atthe a-level of significance.10.1.3 If the number of assessors is less than the value givenin T
39、able 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 analyzethe data obtained from the test. The calculations are as follows:Pc5 c/nScstandard error of Pc! 5 =Pc1Pc! / nconfiden
40、ce 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-risk 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 limi
41、t is less than Pmax, then conclude thatthe samples are similar in attribute intensity (that is, no moreTABLE 3 Number of Selected Responses Needed ForSignificance in a Directional Difference Test, One-SidedAlternativeNOTE 1Entries are the minimum number of common responsesrequired for significance a
42、t the stated significance level (column) for thecorresponding number of assessors n (row). Reject the assumption of “nodifference” if the number of correct responses is greater than or equal tothe tabled value.NOTE 2For values of n not in the table, compute the missing entry asfollows: Minimum numbe
43、r of responses (x) = nearest whole numbergreater thanx=(n/2) + z =n/4 , where z varies with the 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
44、 value as presented in the table,but the difference never exceeds one response. Exact values can beobtained from binomial distribution functions widely available in statis-tical computer packages.NOTE 3Adapted from Meilgaard et al (8).Significance level (%)n .50 .20 .10 .05 .01 .0014 3 4 4 . . .5 4
45、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 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 2
46、025 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 17 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 3
47、652 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 41 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 66E2164085than Pmaxof the population wou
48、ld perceive a difference at theb-level of significance). If the confidence 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 Appendix X4.11. Report11.1 Report
49、 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 should communi-cate that all storage, handling, and preparation was done insuch a way as to yield samples that differed only in the variableof interest, if at all);11.1.3 The number of assessors, the number of selections ofeach
