ASTM E1697-95(1999)
(Test Method)Standard Test Method for Unipolar Magnitude Estimation of Sensory Attributes
Standard Test Method for Unipolar Magnitude Estimation of Sensory Attributes
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 panelists to produce magnitude estimations and statistical evaluation of the estimations.
1.2 Magnitude estimation is a psychophysical scaling technique in which panelists assign numeric values to the magnitude of an attribute. The only constraint placed upon the panelist 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 panelists 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 panelists can properly identify the attribute being evaluated is beyond the scope of this test method.
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Designation: E 1697 – 95 (Reapproved 1999)
Standard Test Method for
Unipolar Magnitude Estimation of Sensory Attributes
This standard is issued under the fixed designation E 1697; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope ISO 3534-3:1985 Statistics—Vocabulary and Symbols—
Part 3: Experimental Design
1.1 This test method describes a procedure for the applica-
ISO 4121:1987 Sensory Analysis—Methodology—
tion of unipolar magnitude estimation to the evaluation of the
Evaluation of Food Products by Methods Using Scales
magnitude of sensory attributes. The test method covers
ISO/DIS 5492:1990 Sensory Analysis—Vocabulary (1)
procedures for the training of panelists to produce magnitude
ISO 6658:1985 Sensory Analysis—Methodology—General
estimations and statistical evaluation of the estimations.
Guidance
1.2 Magnitude estimation is a psychophysical scaling tech-
ISO/DIS 8586-1:1989 Sensory Analysis—Methodology—
nique in which panelists assign numeric values to the magni-
General Guide for Selection, Training and Monitoring
tude of an attribute. The only constraint placed upon the
Subjects—Part 1: Qualifying Subjects (1)
panelist is that the values assigned should conform to a ratio
ISO 8589:1988 Sensory Analysis—General Guidance for
principle. For example, if the attribute seems twice as strong in
the Design of Test Rooms
sample B when compared to sample A, sample B should
receive a value which is twice the value assigned to sampleA.
3. Terminology
1.3 The intensity of attributes such as pleasantness, sweet-
3.1 Definitions:
ness, saltiness or softness can be evaluated using magnitude
3.1.1 external modulus—a number assigned by the panel
estimation.
leadertodescribetheintensityoftheexternalreferencesample
1.4 Magnitude estimation may provide advantages over
or the first sample of the sample set. The external modulus is
other scaling methods, particularly when the number of pan-
sometimes referred to as a “fixed modulus” or just the
elists and the time available for training are limited. With
“modulus.” In this case the reference is said to be modulated.
approximately1hof training, a panel of 15 to 20 naive
3.1.2 external reference sample for magnitude
individuals can produce data of adequate precision and repro-
estimation—a sample designated as the one to which all others
ducibility. Any additional training that may be required to
are to be compared, or to which the first sample of a set is to
ensure that the panelists can properly identify the attribute
be compared, when each subsequent sample in the set is
being evaluated is beyond the scope of this test method.
comparedtotheprecedingsample.Thissampleisnormallythe
2. Referenced Documents first sample to be presented.
3.1.3 internal modulus—a number assigned by the panelist
2.1 ASTM Publications:
2 to describe the intensity of the external reference sample or the
STP 434 Manual on Sensory Testing Methods
first sample of the sample set. The internal modulus is
STP 758 Guidelines for the Selection and Training of
2 sometimes referred to as a “non-fixed modulus.” When an
Sensory Panel Members
internal modulus is used, the reference is sometimes said to be
STP 913 Physical Requirement Guidelines for Sensory
2 unmodulated.
Evaluation Laboratories
3.1.4 internal reference sample for magnitude
2.2 ISO Standards:
estimation—a sample present in the experimental set, which is
ISO 3534:1977 Statistics—Vocabulary and Symbols
presented to the panelist as if it were a test sample. The value
assigned to this sample(s) can be used for normalizing panel-
1 ists’ data. If an external reference is used, the internal refer-
This test method is under the jurisdiction ofASTM Committee E18 on Sensory
ence(s) are normally identical to it.
Evaluation of Materials and Products and is the direct responsibility of Subcom-
mittee E18.03 on Sensory Theory and Statistics.
3.1.5 magnitude estimation—the process of assigning val-
Current edition approved March 15, 1995. Published May 1995.
ues to the intensities of an attribute of products in such a way
Available from ASTM Headquarters.
that the ratios of the values assigned and the panelist’s
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036. perceptions of the attribute are the same.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1697 – 95 (1999)
3.1.6 normalizing—The process of multiplying each panel- 5.3 Magnitudeestimationisnotassusceptibletoend-effects
ist’s raw data by, or adding to the logarithm of each panelist’s as interval scaling techniques. These can occur when panelists
raw data, a value which brings all the data onto a common are not familiar with the entire range of sensations being
scale. Also referred to as rescaling. presented. Under these circumstances, panelists may assign an
3.1.7 Stevens’ Equation or the Psychophysical Power early sample to a category which is too close to one end of the
Function— scale. Subsequently, they may “run out of scale” and be forced
to assign perceptually different samples to the same category.
n
R 5 KS (1)
This should not occur with magnitude estimation, as, in theory,
there are an infinite number of categories.
where:
R = the panelist’s response (the perceived intensity), 5.4 Magnitude estimation is one frequently used technique
K = a constant that reconciles the units of measurement that permits the representation of data in terms of Stevens’
used for R and S,
Power Law.
S = the stimulus (chemical concentration or physical
5.5 The disadvantages of magnitude estimation arise prima-
force), and
rily from the requirements of the data analysis.
n = the exponent of the power function and the slope of
5.5.1 Permitting each panelist to choose a different numeri-
the regression curve for R and S when they are
cal scale may produce significant panelist effects. This disad-
expressed in logarithmic units.
vantage can be overcome in a number of ways, as follows.The
In practice, Stevens’ equation is generally transformed to
experimenter must choose the approach most appropriate for
logarithms, either common or natural
the circumstances.
5.5.1.1 Experiments can be designed such that analysis of
lnR 5 lnK 1 nlnS (2)
variance can be used to remove the panelist effects and
interactions.
4. Summary of Test Method
5.5.1.2 Alternatively, panelists can be forced to a common
4.1 Panelists judge the intensity of an attribute of a set of
scale, either by training or by use of external reference samples
samples, presented in random order, on a ratio scale. For
with assigned values (modulus).
example, if one sample is given a value of 50 and a second
5.5.1.3 Finally, each panelist’s data can be brought to a
sample is twice as strong, it will be given a value of 100. If it
common scale by one of a variety of normalizing methods.
is half as strong it will be given a value of 25. There are three
5.5.2 Logarithms must be applied before carrying out data
procedures that can be used.
analysis. This becomes problematic if values are near thresh-
4.1.1 Panelists are instructed to assign any value to describe
old, as a logarithm of zero cannot be taken. (See 11.2.1)
the intensity of the first sample (external reference, which may
5.6 Magnitude estimation should be used:
or may not be part of the sample set). Panelists then rate the
5.6.1 When end-effects are a concern, for example when
intensityofthefollowingsamplesinrelationtothevalueofthe
panelists are not familiar with the entire range of sensations
external reference.
being presented.
4.1.2 The external reference is pre-assigned a value (modu-
5.6.2 WhenStevens’PowerLawistobeappliedtothedata.
lus) to describe its intensity by the panel leader. Panelists rate
5.6.3 Generally, in central location testing with panelists
theintensityofthefollowingsamplesinrelationtotheexternal
trained in the technique. It is not appropriate for home use or
reference and the modulus.
mall intercept testing with consumers.
4.1.3 Panelists rate the intensity of each subsequent sample
5.7 This test method is only meant to be used with panelists
in relation to the preceding sample. The first sample of the set
who are specifically trained in magnitude estimation. Do not
may or may not have a modulus.
use this method with untrained panelists or untrained consum-
4.2 Individual judgments can be converted to a common
ers.
scale by normalizing the data. Three normalizing methods can
be used: internal standard normalizing, external calibration
6. Conditions of Testing
and, if a modulus is not used, no standard normalizing (method
6.1 The general conditions for testing, such as the location,
of averages). See 11.4 and Appendix X2-Appendix X4.
preparations, presentation and coding of samples, and the
4.3 Results are averaged using geometric means. Analysis
selection and training of panelists are described in the stan-
of variance or other statistical analyses may be performed after
dards for general methodology, such as ISO 6658, ISO 8586-1,
the data have been converted to logarithms.
ISO 8589, ASTM STPs 434, 758, 913 or those describing
methods using scales and categories, for example, ISO 4121
5. Significance and Use
and ASTM STP 434.
5.1 Magnitude estimation may be used to measure and
7. Selection and Training of Panelists
compare the intensities of attributes of a wide variety of
products. 7.1 Refer to ISO 8586-1 or ASTM STP 758 for all the
5.2 Magnitude estimation provides a large degree of flex- general considerations concerning the selection and training of
ibility for both the experimenter and the panelist. Once trained panelists.
in magnitude estimation, panelists are generally able to apply 7.2 As is true for all methods of sensory evaluation, the
their skill to a wide variety of sample types and attributes, with panel leader will have to make judgments as to the level of
minimal additional training. proficiency required of the panelists.The objectives of the test,
E 1697 – 95 (1999)
the availability of panelists, the costs of securing additional effects, that is, their responses are affected by the order in
panelists and of additional training should all be considered in whichtheyevaluatethesamples.Theyshouldbereassuredthat
the design of a training program. Panelists generally reach a despite individual order effects, the group’s results will be
stable level of proficiency in the method itself after three to accurate.
four exercises in assigning magnitudes. 7.8 If the panelists’ results are very different, review the
7.3 Estimating the areas of geometric shapes has proven principles of the method again. If the panel leader judges that
very useful for introducing panelists to the basic concepts of a panelist cannot be trained in the method, the training should
magnitude estimation. A set of 18 figures composed of six be discontinued at this point and the panelist excused.
circles, six equilateral triangles and six squares ranging in size 7.9 Once the panel has successfully completed the area
2 2
from approximately 2 cm to 200 cm has been used estimation exercise, further training should be carried out with
successfully for training panelists (see Table 1). the commodity or type of test substance to be used in the main
7.4 Prior to presenting the figures, the panel leader instructs trial(s). This gives the panelist experience in applying magni-
the candidate in the principles of the method. This instruction tude estimation to attributes characterizing the test sample.
should include, but is not necessarily limited to the following 7.10 The panel leader may need to design exercises for
three points. training panelists to properly identify the attributes to be
7.4.1 If the attribute is not present, the value 0 should be evaluated. The need for this will depend on the objectives and
assigned. requirements of the test.
7.4.2 There is no upper limit to the scale.
8. Number of Panelists Required
7.4.3 Values should be assigned on a ratio basis: If the
attribute is twice as intense, it should receive a rating twice as 8.1 As is true for other forms of scaling, the number of
panelists necessary for a given task depends on the complexity
large.
7.5 Panelists have a tendency to use “round numbers” such of the task, how close together the various test samples are in
the attribute being evaluated, the amount of training the
as 5, 10, 20, 25, etc. This should be pointed out explicitly
during training. Panelists should be encouraged, “given per- panelists have received, and the importance to be attached to
the decision based on the test results (c.f., ISO 8586-1). Issues
mission,” to use all numbers. Panelists are also influenced by
the ratios mentioned in training. Therefore, care should be of statistical power need to be resolved based on the variance
associated with a particular evaluation and the magnitude of
taken to mention a variety of different ratios, for example, 3:1
1 1
⁄3 , 7.5, 2.4, not just 2:1 and ⁄2 . the differences that need to be detected.
7.6 Assigning Codes to the Figures— The figures are
9. Reference Samples
presented singly, centered on an 8.5 3 11 in. sheet of white
9.1 External References—The panel leader specifies to the
paper. The panelist states his magnitude estimate; the estima-
panelists that the reference sample has a value of, for example,
tion is recorded. The 8.5-cm square is presented first with the
30, 50, 100 or whatever seems appropriate to the panel leader.
instruction to assign it a value between 30 and 100. The
The leader instructs the panelists to make his or her subsequent
balance of the geometric figures should be shuffled prior to
judgments relative to the value assigned.
each test so that the type of geometric figure and the size of the
9.2 The reference should have an intensity close to the
areas do not form a particular pattern.
geometric mean for the whole panel. A reference that repre-
7.7 Comparing the Results—Aftercompletingthefullsetof
sents an extreme value of the attribute will distort the data due
shape estimates, panelists should be allowed to compare their
to a contrast effect and reduce the sensitivity of the method.
results with the averaged results of the group. If this is not
9.3 Magnitude estimation does not impose any specific
practical, the results from a previous group can also be used.
restrictions on sample presentation. However, the external
The objective is to provide positive feedback, th
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