1、Designation: E 1885 04Standard Test Method forSensory AnalysisTriangle Test1This standard is issued under the fixed designation E 1885; 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 parenthe
2、ses 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 determiningwhether a perceptible sensory difference exists betweensamples of two products.1.2 This test method a
3、pplies whether a difference may existin a single sensory attribute or in several.1.3 This test method is applicable when the nature of thedifference between the samples is unknown. It does notdetermine the size or the direction of the difference. Theattribute(s) responsible for the difference are no
4、t identified.1.4 Compared to the duo-trio test, the triangle test canachieve an equivalent level of statistical significance withfewer assessors. For details on how the triangle test comparesto other three-sample tests, see Refs (1), (2), (3) and (4).21.5 This test method is applicable only if the p
5、roducts arehomogeneous. If two samples of the same product can often bedistinguished, then another method, for example, descriptiveanalysis, may be more appropriate.1.6 This test method is applicable only when the productsdo not cause excessive sensory fatigue, carryover or adapta-tion.1.7 This stan
6、dard does not purport to address all of 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 A
7、STM Standards:3E 253 Terminology Relating to Sensory Evaluation of Ma-terials and ProductsE 456 Terminology for Relating to Quality and StatisticsE 1871 Practice for Serving Protocol for Sensory Evalua-tion of Foods and Beverages2.2 ISO Standard:ISO 4120 Sensory Analysis Methodology TriangularTest43
8、. Terminology3.1 DefinitionsFor definition of terms relating to sensoryanalysis, see Terminology E 253, and for terms relating tostatistics, see Terminology E 456.3.2 Definitions of Terms Specific to This Standard:3.2.1 a (alpha) riskprobability of concluding that a per-ceptible difference exists wh
9、en, in reality, one does not. (Alsoknown as Type I Error or significance level.)3.2.2 b (beta) riskprobability of concluding that no per-ceptible difference exists when, in reality, one does. (Alsoknown as Type II Error.)3.2.3 pcprobability of a correct response.3.2.4 pd(proportion of discriminators
10、)proportion of thepopulation represented by the assessors that can distinguishbetween the two products.3.2.5 productmaterial to be evaluated.3.2.6 sampleunit of product prepared, presented, andevaluated in the test.3.2.7 sensitivitygeneral term used to summarize the per-formance characteristics of t
11、he test. The sensitivity of the testis rigorously defined, in statistical terms, by the values selectedfor a, b, and pd.3.3 triadthree uniquely coded samples given to an asses-sor in the triangle test; two samples are alike (that is, of oneproduct) and one is different (that is, of the other product
12、).4. Summary of Test Method4.1 Clearly define the test objective in writing.4.2 Choose the number of assessors based on the level ofsensitivity desired for the test. The sensitivity of the test is, inpart, a function of two competing risks: the risk of declaringthe samples different when they are no
13、t (that is, a-risk) and therisk of not declaring the samples different when they are (thatis, b-risk). Acceptable values of a and b vary depending on thetest objective and should be determined before the test (seeAppendix X3).1This test method is under the jurisdiction of ASTM Committee E18 on Senso
14、ryEvaluation of Materials and Products and is the direct responsibility of Subcom-mittee E18.04 on Fundamentals of Sensory.Current edition approved Oct. 1, 2004. Published October 2004. Originallyapproved in 1997. Last previous edition approved in 2003 as E 1885 97 (2003).2The boldface numbers given
15、 in parentheses refer to a list of references at theend of the text.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM w
16、ebsite.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3 Assessors receive a triad and are informed that two ofthe samples a
17、re alike and that one is different. The assessorsreport which they believe to be the different, or “odd,” sample,even if the selection is based only on a guess.4.4 Results are tallied and significance determined by ref-erence to a statistical table.5. Significance and Use5.1 This test method is effe
18、ctive for the following testobjectives:5.1.1 To determine whether a perceivable difference resultsor a perceivable difference does not result, for example, whena change is made in ingredients, processing, packaging, han-dling or storage; or5.1.2 To select, train and monitor assessors.5.2 This test m
19、ethod itself does not change whether thepurpose of the triangle test is to determine that two products areperceivably different versus that the products are not perceiv-ably different. Only the selected values of pd, a, and b change.If the objective of the test is to determine if there is aperceivab
20、le difference between two products, then the valueselected for a is typically smaller than the value selected for b.If the objective is to determine if the two products aresufficiently similar to be used interchangeably, then the valueselected for b is typically smaller than the value selected for a
21、and the value of pdis selected to define “sufficiently similar.”6. Apparatus6.1 Carry out the test under conditions that prevent contactbetween assessors until the evaluations have been completedfor example, booths that comply with STP 913 (5).6.2 Sample preparation and serving sizes should complywi
22、th Practice E 1871. See Refs (6) or (7).7. Assessors7.1 All assessors must be familiar with the mechanics of thetriangle test (the format, the task, and the procedure ofevaluation). Experience and familiarity with the product andtest method may increase the sensitivity of an assessor and maytherefor
23、e increase the likelihood of finding a significant differ-ence. Monitoring the performance of assessors over time maybe useful for increased sensitivity.7.2 Choose assessors in accordance with test objectives. Forexample, to project results to a general consumer population,assessors with unknown sen
24、sitivity might be selected. Toincrease protection of product quality, assessors with demon-strated acuity should be selected.7.3 The decision to use trained or untrained assessors shouldbe addressed prior to testing. Training may include a prelimi-nary presentation on the nature of the samples and t
25、he problemconcerned. If the test concerns the detection of particular taint,consider the inclusion of samples during training that demon-strate its presence and absence. Such demonstration willincrease the panels acuity for the taint but may detract fromother differences. See STP 758 for details (8)
26、. Allow adequatetime between the exposure to the training samples and theactual triangle test to avoid carryover.7.4 During the test sessions, avoid giving information aboutproduct identity, expected treatment effects, or individualperformance until all testing is complete.7.5 Pooling multiple evalu
27、ations by the same assessor is notrecommended because results are less representative of thepopulation and the risk of incorrect conclusion is greater.8. Number of Assessors8.1 Choose the number of assessors to yield the level ofsensitivity called for by the test objectives. The sensitivity ofthe te
28、st is a function of three values: the a-risk, and the b-risk,and the maximum allowable proportion of distinguishers, pd.58.2 Prior to conducting the test, select values for a, b andpd. The following can be considered as general guidelines.8.2.1 For a-risk: A statistically significant result at:8.2.1
29、.1 10 to 5 % (0.10 to 0.05) indicates “slight” evidencethat a difference was apparent;8.2.1.2 5 to 1 % (0.05 to 0.01) indicates “moderate” evi-dence that a difference was apparent;8.2.1.3 1 to 0.1 % (0.01 to 0.001) indicates “strong” evi-dence that a difference was apparent; and8.2.1.4 Below 0.1 % (
30、 35 % represent large values.8.3 Having defined the required level of sensitivity for thetest using 8.2, use Table A1.1 to determine the number ofassessors necessary. Enter Table A1.1 in the section corre-sponding to the selected value of pdand the column corre-sponding to the selected value of b. T
31、he minimum requirednumber of assessors is found in the row corresponding to theselected value of a. Alternatively, Table A1.1 can be used todevelop a set of values for pd, a and b that provide acceptablesensitivity while maintaining the number of assessors withinpractical limits. The approach is pre
32、sented in detail in Ref (9).8.4 Often in practice, the number of assessors is determinedby material conditions (for example, duration of the experi-ment, number of available assessors, quantity of product).However, increasing the number of assessors increases thelikelihood of detecting small proport
33、ions of distinguishers.Thus, one should expect to use larger numbers of assessorswhen trying to demonstrate that products are similar comparedto when one is trying to prove they are different. Often 18 to 365In this test method, the probability of a correct response, pdis modeled as pc=1a/bpd+ (1/3)
34、a/b(1-pd), where pdis the proportion of the entire population ofassessors who can distinguish between the two products. It is a strictly statistical“guessing model” of the assessors behavior. It is not a psychometric model of theassessors decision process, such as the Thurstone-Ura model that could
35、also beapplied in discrimination testing.E1885042assessors are used when testing for a difference. For compa-rable sensitivity when testing for similarity, 42 to 78 assessorsare needed.9. Procedure9.1 Prepare worksheets and scoresheets (see Appendix X1-Appendix X3) in advance of the test so as to ut
36、ilize an equalnumber of the six possible sequences of two products, A and B.Distribute these at random in groups of six among thepanelists. The six sequences are:ABB AAB ABABAA BBA BAB9.2 Sometimes the final number of assessors does not endup as a multiple of six. For example, if a test was planned
37、for36 assessors and only 34 actually participated, there would befive complete series of the six sequences and one incompleteset of four in which two of the six triads were randomlydropped.9.3 It is critical to the validity of the test that assessorscannot identify the samples from the way in which
38、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 possible to mask color differences usinglight filters, subdued illumination, or colored ser
39、ving contain-ers. Code the serving containers containing the samples in auniform manner, preferably using three-digit numbers, chosenat random for each test. Prepare samples out of sight and in anidentical manner: same apparatus, same serving containers, andsame quantities of products (see ASTM Serv
40、ing Protocols).9.4 Present each triad simultaneously if possible, followingthe same spatial arrangement for each assessor (on a line to besampled always from left to right, in a triangular array, etc.)Within the triad, assessors are typically allowed to makerepeated evaluations of each sample as des
41、ired. If the condi-tions of the test require the prevention of repeat evaluations forexample, if samples are bulky, leave an aftertaste, or showslight differences in appearance that cannot be masked, presentthe samples sequentially and do not allow repeated evaluations.9.5 Each scoresheet should pro
42、vide for a single triad ofsamples. If a different set of products is to be evaluated by anassessor in a single session, the completed scoresheet and anyremaining product should be returned to the test administratorprior to receiving the subsequent triad. The assessor cannot goback to any of the prev
43、ious samples or change the verdict onany previous test.9.6 Do not ask questions about preference, acceptance, ordegree of difference after the initial selection of the oddsample. The selection the assessor has just made may bias thereply to any additional questions. Responses to such questionsmay be
44、 obtained through separate tests for preference, accep-tance, degree of difference, etc. (see Manual 26) (10).Acomment section asking why the choice was made may beincluded for the assessors remarks.9.7 The triangle test is a forced-choice procedure; assessorsare not allowed the option of reporting
45、“no difference.” Anassessor who detects no difference between the samples shouldbe instructed to randomly select one of the samples as being theodd one and can indicate that the selection was only a guess inthe comments section of the scoresheet.10. Analysis and Interpretation of Results10.1 Use Tab
46、le A1.2 to analyze the data obtained from atriangle test. The actual number of assessors can be greater thanthe minimum value given in Table A1.1. If the number ofcorrect responses is greater than or equal to the number givenin Table A1.2, conclude that a perceptible difference existsbetween the sam
47、ples. If the number of correct responses is lessthan the number given in Table A1.2, conclude that the samplesare sufficiently similar. Again, the conclusions are based on therisks accepted when the level of sensitivity (that is, pd, a, andb) was selected in determining the number of assessors.10.2
48、If desired, calculate a confidence interval on theproportion of the population that can distinguish the samples.This method is described in Appendix X4.11. Report11.1 Report the test objective, the results, and the conclu-sions. The following additional information is recommended:11.1.1 The purpose
49、of the test and the nature of thetreatment studied;11.1.2 Full Identification of the SamplesOrigin, methodof preparation, quantity, shape, storage prior to testing, servingsize, temperature. (Sample information should communicatethat all storage handling, and preparation was done in such away as to yield samples that differ only due to the variable ofinterest, if at all);11.1.3 The number of assessors, the number of correctselections, and the result of the statistical evaluation;11.1.4 AssessorsAge, gender, experience in sensory test-ing, with the product, with the
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