ASTM E1697-05(2012)e1
(Test Method)Standard Test Method for Unipolar Magnitude Estimation of Sensory Attributes
Standard Test Method for Unipolar Magnitude Estimation of Sensory Attributes
SIGNIFICANCE AND USE
Magnitude estimation may be used to measure and compare the intensities of attributes of a wide variety of products.
Magnitude estimation provides a large degree of flexibility for both the experimenter and the assessor. Once trained in magnitude estimation, assessors are generally able to apply their skill to a wide variety of sample types and attributes, with minimal additional training.
Magnitude estimation is not as susceptible to end-effects as interval scaling techniques. These can occur when assessors are not familiar with the entire range of sensations being presented. Under these circumstances, assessors may assign an early sample to a category which is too close to one end of the scale. Subsequently, they may “run out of scale” and be forced to 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.
Magnitude estimation is one frequently used technique that permits the representation of data in terms of Stevens' Power Law.
The disadvantages of magnitude estimation arise primarily from the requirements of the data analysis.
Permitting each assessor to choose a different numerical scale may produce significant assessor effects. This disadvantage can be overcome in a number of ways, as follows. The experimenter must choose the approach most appropriate for the circumstances.
Experiments can be designed such that analysis of variance can be used to remove the assessor effects and interactions.
Alternatively, assessors can be forced to a common scale, either by training or by use of external reference samples with assigned values (modulus).
Finally, each assessor's data can be brought to a common scale by one of a variety of normalizing methods.
Logarithms must be applied before carrying out data analysis. This becomes problematic if values are near threshold, as a logarithm of zero cannot be taken (see 11.2.1).
Magnitude estimatio...
SCOPE
1.1 This test method describes a procedure for the application of unipolar magnitude estimation to the evaluation of the magnitude of sensory attributes. The test method covers procedures for the training of assessors to produce magnitude estimations and statistical evaluation of the estimations.
1.2 Magnitude estimation is a psychophysical scaling technique in which assessors assign numeric values to the magnitude of an attribute. The only constraint placed upon the assessor is that the values assigned should conform to a ratio principle. For example, if the attribute seems twice as strong in sample B when compared to sample A, sample B should receive a value which is twice the value assigned to sample A.
1.3 The intensity of attributes such as pleasantness, sweetness, saltiness or softness can be evaluated using magnitude estimation.
1.4 Magnitude estimation may provide advantages over other scaling methods, particularly when the number of assessors and the time available for training are limited. With approximately 1 h of training, a panel of 15 to 20 naive individuals can produce data of adequate precision and reproducibility. Any additional training that may be required to ensure that the assessors can properly identify the attribute being evaluated is beyond the scope of this test method.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
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Designation: E1697 − 05 (Reapproved 2012)
Standard Test Method for
Unipolar Magnitude Estimation of Sensory Attributes
This standard is issued under the fixed designation E1697; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorially corrected 11.3 and changed “panelist” to “assessor” throughout in August 2012.
1. Scope 2.2 ASTM Publications:
Manual 26Sensory Testing Methods, 2nd Edition
1.1 This test method describes a procedure for the applica-
STP758 Guidelines for the Selection and Training of
tion of unipolar magnitude estimation to the evaluation of the
Sensory Panel Members
magnitude of sensory attributes. The test method covers
2.3 ISO Standards:
procedures for the training of assessors to produce magnitude
ISO 11056:1999 Sensory Analysis—Methodology—
estimations and statistical evaluation of the estimations.
Magnitude Estimation Method
1.2 Magnitude estimation is a psychophysical scaling tech-
ISO 4121:1987 Sensory Analysis—Methodology—
nique in which assessors assign numeric values to the magni-
Evaluation of Food Products by Methods Using Scales
tude of an attribute. The only constraint placed upon the
ISO/DIS5492:1990Sensory Analysis—Vocabulary (1)
assessor is that the values assigned should conform to a ratio
ISO6658:1985Sensory Analysis—Methodology—General
principle.Forexample,iftheattributeseemstwiceasstrongin
Guidance
sample B when compared to sample A, sample B should
ISO/DIS8586-1:1989 Sensory Analysis—Methodology—
receive a value which is twice the value assigned to sampleA.
General Guide for Selection, Training and Monitoring
1.3 The intensity of attributes such as pleasantness, Subjects—Part 1: Qualifying Subjects (1)
sweetness, saltiness or softness can be evaluated using magni- ISO8589:1988Sensory Analysis—General Guidance for
tude estimation. the Design of Test Rooms
1.4 Magnitude estimation may provide advantages over
3. Terminology
other scaling methods, particularly when the number of asses-
3.1 Definitions:
sors and the time available for training are limited. With
3.1.1 external modulus—number assigned by the panel
approximately1hof training, a panel of 15 to 20 naive
leadertodescribetheintensityoftheexternalreferencesample
individuals can produce data of adequate precision and repro-
or the first sample of the sample set. The external modulus is
ducibility. Any additional training that may be required to
sometimes referred to as a “fixed modulus” or just the
ensure that the assessors can properly identify the attribute
“modulus.” In this case the reference is said to be modulated.
being evaluated is beyond the scope of this test method.
3.1.2 external reference sample for magnitude estimation—
2. Referenced Documents
sample designated as the one to which all others are to be
compared, or to which the first sample of a set is to be
2.1 ASTM Standards:
compared,wheneachsubsequentsampleinthesetiscompared
E253Terminology Relating to Sensory Evaluation of Mate-
to the preceding sample. This sample is normally the first
rials and Products
sample to be presented.
E1871GuideforServingProtocolforSensoryEvaluationof
Foods and Beverages
3.1.3 internal modulus—numberassignedbytheassessorto
describe the intensity of the external reference sample or the
first sample of the sample set. The internal modulus is
ThistestmethodisunderthejurisdictionofASTMCommitteeE18onSensory
sometimes referred to as a “non-fixed modulus.” When an
Evaluation and is the direct responsibility of Subcommittee E18.03 on Sensory
internal modulus is used, the reference is sometimes said to be
Theory and Statistics.
unmodulated.
Current edition approved Aug. 1, 2012. Published August 2012. Originally
approved in 1995. Last previous edition approved in 2005 as E1697–05. DOI:
10.1520/E1697-05R12E01.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available from ASTM Headquarters, 100 Barr Harbor Drive, PO Box C700,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM West Conshohocken, PA 19428–29593.
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E1697 − 05 (2012)
3.1.4 internal reference sample for magnitude estimation— 4.3 Results are averaged using geometric means. Analysis
sample present in the experimental set, which is presented to ofvarianceorotherstatisticalanalysesmaybeperformedafter
the assessor as if it were a test sample. The value assigned to the data have been converted to logarithms.
this sample(s) can be used for normalizing assessors’ data. If
an external reference is used, the internal reference(s) are
5. Significance and Use
normally identical to it.
5.1 Magnitude estimation may be used to measure and
3.1.5 magnitude estimation—process of assigning values to
compare the intensities of attributes of a wide variety of
theintensitiesofanattributeofproductsinsuchawaythatthe
products.
ratios of the values assigned and the assessor’s perceptions of
5.2 Magnitude estimation provides a large degree of flex-
the attribute are the same.
ibilityforboththeexperimenterandtheassessor.Oncetrained
3.1.6 normalizing—process of multiplying each assessor’s
in magnitude estimation, assessors are generally able to apply
raw data by, or adding to the logarithm of each assessor’s raw
theirskilltoawidevarietyofsampletypesandattributes,with
data, a value which brings all the data onto a common scale.
minimal additional training.
Also referred to as rescaling.
5.3 Magnitudeestimationisnotassusceptibletoend-effects
3.1.7 Stevens’ Equation or the Psychophysical Power
as interval scaling techniques.These can occur when assessors
Function—
are not familiar with the entire range of sensations being
n
R 5 KS (1)
presented.Underthesecircumstances,assessorsmayassignan
early sample to a category which is too close to one end of the
where:
scale. Subsequently, they may “run out of scale” and be forced
R = the assessor’s response (the perceived intensity),
to assign perceptually different samples to the same category.
K = a constant that reconciles the units of measurement
Thisshouldnotoccurwithmagnitudeestimation,as,intheory,
used for R and S,
there are an infinite number of categories.
S = the stimulus (chemical concentration or physical
force), and
5.4 Magnitude estimation is one frequently used technique
n = theexponentofthepowerfunctionandtheslopeofthe
that permits the representation of data in terms of Stevens’
regression curve for R and S when they are expressed
Power Law.
in logarithmic units.
5.5 The disadvantages of magnitude estimation arise pri-
In practice, Stevens’ equation is generally transformed to
marily from the requirements of the data analysis.
logarithms, either common or natural:
5.5.1 Permitting each assessor to choose a different numeri-
lnR 5 lnK1nlnS (2)
cal scale may produce significant assessor effects. This disad-
vantagecanbeovercomeinanumberofways,asfollows.The
3.2 Reference Terminology E253 for general definitions
experimenter must choose the approach most appropriate for
related to sensory evaluation.
the circumstances.
4. Summary of Test Method
5.5.1.1 Experiments can be designed such that analysis of
variance can be used to remove the assessor effects and
4.1 Assessors judge the intensity of an attribute of a set of
interactions.
samples, presented in random order, on a ratio scale. For
5.5.1.2 Alternatively, assessors can be forced to a common
example, if one sample is given a value of 50 and a second
sample is twice as strong, it will be given a value of 100. If it scale,eitherbytrainingorbyuseofexternalreferencesamples
with assigned values (modulus).
is half as strong it will be given a value of 25. There are three
procedures that can be used.
5.5.1.3 Finally, each assessor’s data can be brought to a
4.1.1 Assessors are instructed to assign any value to de- common scale by one of a variety of normalizing methods.
scribe the intensity of the first sample (external reference,
5.5.2 Logarithms must be applied before carrying out data
which may or may not be part of the sample set). Assessors
analysis. This becomes problematic if values are near
then rate the intensity of the following samples in relation to
threshold, as a logarithm of zero cannot be taken (see 11.2.1).
the value of the external reference.
5.6 Magnitude estimation should be used:
4.1.2 The external reference is pre-assigned a value (modu-
5.6.1 When end-effects are a concern, for example when
lus) to describe its intensity by the panel leader.Assessors rate
assessors are not familiar with the entire range of sensations
theintensityofthefollowingsamplesinrelationtotheexternal
being presented.
reference and the modulus.
5.6.2 WhenStevens’PowerLawistobeappliedtothedata.
4.1.3 Assessorsratetheintensityofeachsubsequentsample
5.6.3 Generally, in central location testing with assessors
in relation to the preceding sample. The first sample of the set
trained in the technique. It is not appropriate for home use or
may or may not have a modulus.
mall intercept testing with consumers.
4.2 Individual judgments can be converted to a common
scale by normalizing the data. Three normalizing methods can 5.7 Thistestmethodisonlymeanttobeusedwithassessors
be used: internal standard normalizing, external calibration who are specifically trained in magnitude estimation. Do not
and,ifamodulusisnotused,nostandardnormalizing(method use this method with untrained assessors or untrained consum-
of averages). See 11.4 and Appendix X2-Appendix X4. ers.
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E1697 − 05 (2012)
6. Conditions of Testing should be taken to mention a variety of different ratios, for
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example, 3:1 and ⁄3, 7.5, 2.4, not just 2:1 and ⁄2 .
6.1 The general conditions for testing, such as the location,
preparations, presentation and coding of samples, and the
7.6 Assigning Codes to the Figures—The figures are pre-
selection and training of assessors are described in the stan-
sented singly, centered on an 8.5×11 in. sheet of white paper.
dards for general methodology, such as ISO 6658, ISO/DIS
The assessor states his magnitude estimate; the estimation is
8586-1, ISO 8589, ASTM STP758 or those describing meth-
recorded.The 8.5-cm square is presented first with the instruc-
ods using scales and categories, for example, ISO 4121 and
tiontoassignitavaluebetween30and100.Thebalanceofthe
ASTM Manual 26, and for specific serving protocols in Guide
geometric figures should be shuffled prior to each test so that
E1871.
the type of geometric figure and the size of the areas do not
form a particular pattern.
7. Selection and Training of Assessors
7.7 Comparing the Results—Aftercompletingthefullsetof
7.1 Refer to ISO 8586-1 or ASTM STP758 for all the
shape estimates, assessors should be allowed to compare their
general considerations concerning the selection and training of
results with the averaged results of the group. If this is not
assessors. Refer to ISO 11056 for considerations specific to
practical, the results from a previous group can also be used.
magnitude estimation.
The objective is to provide positive feedback, that is, to
7.2 As is true for all methods of sensory evaluation, the
reassure the assessors that they understand the exercise. Care
panel leader will have to make judgments as to the level of
should be taken not to create the impression that there is a
proficiencyrequiredoftheassessors.Theobjectivesofthetest,
“right” answer. Unless their results are very different, depar-
the availability of assessors, the costs of securing additional
tures from the group results should be explained as order
assessors and of additional training should all be considered in
effects, that is, their responses are affected by the order in
the design of a training program. Assessors generally reach a
whichtheyevaluatethesamples.Theyshouldbereassuredthat
stable level of proficiency in the method itself after three to
despite individual order effects, the group’s results will be
four exercises in assigning magnitudes.
accurate.
7.3 Estimating the areas of geometric shapes has proven
very useful for introducing assessors to the basic concepts of 7.8 If the assessors’ results are very different, review the
magnitude estimation. A set of 18 figures composed of six
principles of the method again. If the panel leader judges that
circles, six equilateral triangles and six squares ranging in size
a assessor cannot be trained in the method, the training should
2 2
from approximately 2 cm to 200 cm has been used success-
be discontinued at this point and the assessor excused.
fully for training assessors (see Table 1).
7.9 Once the panel has successfully completed the area
7.4 Prior to presenting the figures, the panel leader instructs
estimation exercise, further training should be carried out with
the candidate in the principles of the method. This instruction
the commodity or type of test substance to be used in the main
should include, but is not necessarily limited to the following
trial(s). This gives the assessor experience in applying magni-
three points.
tude estimation to attributes characterizing the test sample.
7.4.1 If the attribute is not present, the value 0 should be
7.10 The panel leader may need to design exercises for
assigned.
training assessors to properly identify the attributes to be
7.4.2 There is no upper limit to the scale.
evaluated. The need for this will depend on the objectives and
7.4.3 Values should be assigned on a ratio basis: if the
requirements of the test.
attribute is twice as intense, it should receive a rating twice as
large.
8. Number of Assessors Required
7.5 Assessorshaveatendencytouse“roundnumbers”such
as 5, 10, 20, 25, and so forth. This should be pointed out
8.1 As is true for other forms of scaling, the number of
explicitly during training. Assessors should be encouraged,
assessorsnecessaryforagiventaskdependsonthecomplexity
“given permission,” to use all numbers. Assessors are also
of the task, how close together the various test samples are in
influenced by the ratios mentioned in training. Therefore, care
the attribute being evaluated, the amount of training the
assessors have received, and the importance to be attached to
the decision based on the test results (c.f., ISO 8586-1). Issues
TABLE 1 Training Exercise Shapes
of s
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