1、Designation: E1697 05 (Reapproved 2012)1Standard Test Method forUnipolar Magnitude Estimation of Sensory Attributes1This standard is issued under the fixed designation E1697; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEEditorially corrected 11.3 and changed “panelist” to “assessor” throughout in August 2012.1. Scope1.1 This test method de
3、scribes a procedure for the applica-tion of unipolar magnitude estimation to the evaluation of themagnitude of sensory attributes. The test method coversprocedures for the training of assessors to produce magnitudeestimations and statistical evaluation of the estimations.1.2 Magnitude estimation is
4、a psychophysical scaling tech-nique in which assessors assign numeric values to the magni-tude of an attribute. The only constraint placed upon theassessor is that the values assigned should conform to a ratioprinciple. For example, if the attribute seems twice as strong insample B when compared to
5、sample A, sample B shouldreceive a value which is twice the value assigned to sample A.1.3 The intensity of attributes such as pleasantness, sweet-ness, saltiness or softness can be evaluated using magnitudeestimation.1.4 Magnitude estimation may provide advantages overother scaling methods, particu
6、larly when the number of asses-sors and the time available for training are limited. Withapproximately1hoftraining, a panel of 15 to 20 naiveindividuals can produce data of adequate precision and repro-ducibility. Any additional training that may be required toensure that the assessors can properly
7、identify the attributebeing evaluated is beyond the scope of this test method.2. Referenced Documents2.1 ASTM Standards:2E253 Terminology Relating to Sensory Evaluation of Ma-terials and ProductsE1871 Guide for Serving Protocol for Sensory Evaluationof Foods and Beverages2.2 ASTM Publications:3Manua
8、l 26 Sensory Testing Methods, 2nd EditionSTP 758 Guidelines for the Selection and Training ofSensory Panel Members2.3 ISO Standards:4ISO 11056:1999 Sensory AnalysisMethodologyMagnitude Estimation MethodISO 4121:1987 Sensory AnalysisMethodologyEvaluation of Food Products by Methods Using ScalesISO/DI
9、S 5492:1990 Sensory AnalysisVocabulary (1)ISO 6658:1985 Sensory AnalysisMethodologyGeneralGuidanceISO/DIS 8586-1:1989 Sensory AnalysisMethodologyGeneral Guide for Selection, Training and MonitoringSubjectsPart 1: Qualifying Subjects (1)ISO 8589:1988 Sensory AnalysisGeneral Guidance forthe Design of
10、Test Rooms3. Terminology3.1 Definitions:3.1.1 external modulusnumber assigned by the panelleader to describe the intensity of the external reference sampleor the first sample of the sample set. The external modulus issometimes referred to as a “fixed modulus” or just the“modulus.” In this case the r
11、eference is said to be modulated.3.1.2 external reference sample for magnitude estimationsample designated as the one to which all others are to becompared, or to which the first sample of a set is to becompared, when each subsequent sample in the set is comparedto the preceding sample. This sample
12、is normally the firstsample to be presented.3.1.3 internal modulusnumber assigned by the assessor todescribe the intensity of the external reference sample or thefirst sample of the sample set. The internal modulus issometimes referred to as a “non-fixed modulus.” When aninternal modulus is used, th
13、e reference is sometimes said to beunmodulated.1This test method is under the jurisdiction ofASTM Committee E18 on SensoryEvaluation and is the direct responsibility of Subcommittee E18.03 on SensoryTheory and Statistics.Current edition approved Aug. 1, 2012. Published August 2012. Originallyapprove
14、d in 1995. Last previous edition approved in 2005 as E1697 05. DOI:10.1520/E1697-05R12E01.2For 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 Sum
15、mary page onthe ASTM website.3Available from ASTM Headquarters, 100 Barr Harbor Drive, PO Box C700,West Conshohocken, PA 1942829593.4Available 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
16、C700, West Conshohocken, PA 19428-2959, United States.3.1.4 internal reference sample for magnitude estimationsample present in the experimental set, which is presented tothe assessor as if it were a test sample. The value assigned tothis sample(s) can be used for normalizing assessors data. Ifan ex
17、ternal reference is used, the internal reference(s) arenormally identical to it.3.1.5 magnitude estimationprocess of assigning values tothe intensities of an attribute of products in such a way that theratios of the values assigned and the assessors perceptions ofthe attribute are the same.3.1.6 nor
18、malizingprocess of multiplying each assessorsraw data by, or adding to the logarithm of each assessors rawdata, a value which brings all the data onto a common scale.Also referred to as rescaling.3.1.7 Stevens Equation or the Psychophysical PowerFunctionR 5 KSn(1)where:R = the assessors response (th
19、e perceived intensity),K = a constant that reconciles the units of measurementused for R and S,S = the stimulus (chemical concentration or physicalforce), andn = the exponent of the power function and the slope ofthe regression curve for R and S when they areexpressed in logarithmic units.In practic
20、e, Stevens equation is generally transformed tologarithms, either common or natural:lnR 5 lnK 1 nlnS (2)3.2 Reference Terminology E253 for general definitionsrelated to sensory evaluation.4. Summary of Test Method4.1 Assessors judge the intensity of an attribute of a set ofsamples, presented in rand
21、om order, on a ratio scale. Forexample, if one sample is given a value of 50 and a secondsample is twice as strong, it will be given a value of 100. If itis half as strong it will be given a value of 25. There are threeprocedures that can be used.4.1.1 Assessors are instructed to assign any value to
22、 de-scribe the intensity of the first sample (external reference,which may or may not be part of the sample set). Assessorsthen rate the intensity of the following samples in relation tothe value of the external reference.4.1.2 The external reference is pre-assigned a value (modu-lus) to describe it
23、s intensity by the panel leader. Assessors ratethe intensity of the following samples in relation to the externalreference and the modulus.4.1.3 Assessors rate the intensity of each subsequent samplein relation to the preceding sample. The first sample of the setmay or may not have a modulus.4.2 Ind
24、ividual judgments can be converted to a commonscale by normalizing the data. Three normalizing methods canbe used: internal standard normalizing, external calibrationand, if a modulus is not used, no standard normalizing (methodof averages). See 11.4 and Appendix X2-Appendix X4.4.3 Results are avera
25、ged using geometric means. Analysisof variance or other statistical analyses may be performed afterthe data have been converted to logarithms.5. Significance and Use5.1 Magnitude estimation may be used to measure andcompare the intensities of attributes of a wide variety ofproducts.5.2 Magnitude est
26、imation provides a large degree of flex-ibility for both the experimenter and the assessor. Once trainedin magnitude estimation, assessors are generally able to applytheir skill to a wide variety of sample types and attributes, withminimal additional training.5.3 Magnitude estimation is not as susce
27、ptible to end-effectsas interval scaling techniques. These can occur when assessorsare not familiar with the entire range of sensations beingpresented. Under these circumstances, assessors may assign anearly sample to a category which is too close to one end of thescale. Subsequently, they may “run
28、out of scale” and be forcedto assign perceptually different samples to the same category.This should not occur with magnitude estimation, as, in theory,there are an infinite number of categories.5.4 Magnitude estimation is one frequently used techniquethat permits the representation of data in terms
29、 of StevensPower Law.5.5 The disadvantages of magnitude estimation arise pri-marily from the requirements of the data analysis.5.5.1 Permitting each assessor to choose a different numeri-cal scale may produce significant assessor effects. This disad-vantage can be overcome in a number of ways, as fo
30、llows. Theexperimenter must choose the approach most appropriate forthe circumstances.5.5.1.1 Experiments can be designed such that analysis ofvariance can be used to remove the assessor effects andinteractions.5.5.1.2 Alternatively, assessors can be forced to a commonscale, either by training or by
31、 use of external reference sampleswith assigned values (modulus).5.5.1.3 Finally, each assessors data can be brought to acommon scale by one of a variety of normalizing methods.5.5.2 Logarithms must be applied before carrying out dataanalysis. This becomes problematic if values are near thresh-old,
32、as a logarithm of zero cannot be taken (see 11.2.1).5.6 Magnitude estimation should be used:5.6.1 When end-effects are a concern, for example whenassessors are not familiar with the entire range of sensationsbeing presented.5.6.2 When Stevens Power Law is to be applied to the data.5.6.3 Generally, i
33、n central location testing with assessorstrained in the technique. It is not appropriate for home use ormall intercept testing with consumers.5.7 This test method is only meant to be used with assessorswho are specifically trained in magnitude estimation. Do notuse this method with untrained assesso
34、rs or untrained consum-ers.6. Conditions of Testing6.1 The general conditions for testing, such as the location,preparations, presentation and coding of samples, and theE1697 05 (2012)12selection and training of assessors are described in the stan-dards for general methodology, such as ISO 6658, ISO
35、/DIS8586-1, ISO 8589, ASTM STP 758 or those describingmethods using scales and categories, for example, ISO 4121and ASTM Manual 26, and for specific serving protocols inGuide E1871.7. Selection and Training of Assessors7.1 Refer to ISO 8586-1 or ASTM STP 758 for all thegeneral considerations concern
36、ing the selection and training ofassessors. Refer to ISO 11056 for considerations specific tomagnitude estimation.7.2 As is true for all methods of sensory evaluation, thepanel leader will have to make judgments as to the level ofproficiency required of the assessors. The objectives of the test,the
37、availability of assessors, the costs of securing additionalassessors and of additional training should all be considered inthe design of a training program. Assessors generally reach astable level of proficiency in the method itself after three tofour exercises in assigning magnitudes.7.3 Estimating
38、 the areas of geometric shapes has provenvery useful for introducing assessors to the basic concepts ofmagnitude estimation. A set of 18 figures composed of sixcircles, six equilateral triangles and six squares ranging in sizefrom approximately 2 cm2to 200 cm2has been used success-fully for training
39、 assessors (see Table 1).7.4 Prior to presenting the figures, the panel leader instructsthe candidate in the principles of the method. This instructionshould include, but is not necessarily limited to the followingthree points.7.4.1 If the attribute is not present, the value 0 should beassigned.7.4.
40、2 There is no upper limit to the scale.7.4.3 Values should be assigned on a ratio basis: if theattribute is twice as intense, it should receive a rating twice aslarge.7.5 Assessors have a tendency to use “round numbers” suchas 5, 10, 20, 25, and so forth. This should be pointed outexplicitly during
41、training. Assessors should be encouraged,“given permission,” to use all numbers. Assessors are alsoinfluenced by the ratios mentioned in training. Therefore, careshould be taken to mention a variety of different ratios, forexample, 3:1 and13 , 7.5, 2.4, not just 2:1 and12 .7.6 Assigning Codes to the
42、 FiguresThe figures are pre-sented singly, centered on an 8.5 3 11 in. sheet of white paper.The assessor states his magnitude estimate; the estimation isrecorded. The 8.5-cm square is presented first with the instruc-tion to assign it a value between 30 and 100. The balance of thegeometric figures s
43、hould be shuffled prior to each test so thatthe type of geometric figure and the size of the areas do notform a particular pattern.7.7 Comparing the ResultsAfter completing the full set ofshape estimates, assessors should be allowed to compare theirresults with the averaged results of the group. If
44、this is notpractical, the results from a previous group can also be used.The objective is to provide positive feedback, that is, toreassure the assessors that they understand the exercise. Careshould be taken not to create the impression that there is a“right” answer. Unless their results are very d
45、ifferent, depar-tures from the group results should be explained as ordereffects, that is, their responses are affected by the order inwhich they evaluate the samples. They should be reassured thatdespite individual order effects, the groups results will beaccurate.7.8 If the assessors results are v
46、ery different, review theprinciples of the method again. If the panel leader judges thata assessor cannot be trained in the method, the training shouldbe discontinued at this point and the assessor excused.7.9 Once the panel has successfully completed the areaestimation exercise, further training sh
47、ould be carried out withthe commodity or type of test substance to be used in the maintrial(s). This gives the assessor experience in applying magni-tude estimation to attributes characterizing the test sample.7.10 The panel leader may need to design exercises fortraining assessors to properly ident
48、ify the attributes to beevaluated. The need for this will depend on the objectives andrequirements of the test.8. Number of Assessors Required8.1 As is true for other forms of scaling, the number ofassessors necessary for a given task depends on the complexityof the task, how close together the vari
49、ous test samples are inthe attribute being evaluated, the amount of training theassessors have received, and the importance to be attached tothe decision based on the test results (c.f., ISO 8586-1). Issuesof statistical power need to be resolved based on the varianceassociated with a particular evaluation and the magnitude ofthe differences that need to be detected.9. Reference Samples9.1 External ReferencesThe panel leader specifies to theassessors that the reference sample has a value of, for example,30, 50, 100 or whatever seems appropriat
