ASTM E1697-05(2020)

Standard Test Method for Unipolar Magnitude Estimation of Sensory Attributes

SIGNIFICANCE AND USE
5.1 Magnitude estimation may be used to measure and compare the intensities of attributes of a wide variety of products.  
5.2 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.  
5.3 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.  
5.4 Magnitude estimation is one frequently used technique that permits the representation of data in terms of Stevens' Power Law.  
5.5 The disadvantages of magnitude estimation arise primarily from the requirements of the data analysis.  
5.5.1 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.
5.5.1.1 Experiments can be designed such that analysis of variance can be used to remove the assessor effects and interactions.
5.5.1.2 Alternatively, assessors can be forced to a common scale, either by training or by use of external reference samples with assigned values (modulus).
5.5.1.3 Finally, each assessor's data can be brought to a common scale by one of a variety of normalizing methods.  
5.5.2 Logarithms must be applied before carrying out data analysis. This becomes problematic if values are near threshold, as a logarit...
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.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Jan-2020
• ICS: 67.240 - Sensory analysis
• Technical Committee: E18 - Sensory Evaluation
• Drafting Committee: E18.03 - Sensory Theory and Statistics

Relations

• Replaces: ASTM E1697-05(2012)e1 - Standard Test Method for Unipolar Magnitude Estimation of Sensory Attributes
• Effective Date: 01-Feb-2020
• Refers: ASTM E253-19 - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 15-Oct-2019
• Refers: ASTM E253-18a - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-Oct-2018
• Refers: ASTM E253-18 - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 15-Jun-2018
• Refers: ASTM E1871-17 - Standard Guide for Serving Protocol for Sensory Evaluation of Foods and Beverages
• Effective Date: 01-Sep-2017
• Refers: ASTM E253-17 - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-May-2017
• Refers: ASTM E253-16 - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-Jun-2016
• Refers: ASTM E253-15b - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-Dec-2015
• Refers: ASTM E253-15a - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-Jun-2015
• Refers: ASTM E253-15 - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 15-Jan-2015
• Refers: ASTM E253-13a - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-Nov-2013
• Refers: ASTM E253-13 - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-May-2013
• Refers: ASTM E253-12a - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-Nov-2012
• Refers: ASTM E253-12 - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-May-2012
• Refers: ASTM E253-11a - Standard Terminology Relating to Sensory Evaluation of Materials and Products
• Effective Date: 01-Dec-2011

Overview

ASTM E1697-05(2020), Standard Test Method for Unipolar Magnitude Estimation of Sensory Attributes, developed by ASTM International, provides a robust and flexible methodology for measuring and comparing the intensities of sensory attributes in a wide range of products. This test method outlines step-by-step procedures for training assessors, performing magnitude estimation, and statistically evaluating sensory data. Unipolar magnitude estimation is widely used in sensory analysis for food, beverages, perfumes, and other consumer products, allowing for precise scaling of sensory perceptions such as sweetness, saltiness, softness, and pleasantness.

Key Topics

• Magnitude Estimation Technique: Assesses the perceived intensity of attributes by assigning numeric values on a ratio scale.
• Unipolar Scaling: Focuses on attributes that range from zero (not present) to increasing levels of intensity, with no negative values.
• Assessor Training: Offers guidance on selecting and training panelists to accurately carry out magnitude estimations, ensuring data reliability with minimal training time.
• Flexibility in Evaluation: Once trained, assessors can apply this method to various attributes and samples with little additional instruction, increasing efficiency in sensory labs.
• Reduction of Scaling Bias: Mitigates end-effects common in interval scaling by allowing infinite category options, thus avoiding scale limitations.
• Data Analysis Requirements: Highlights the need for specialized data handling, including normalization of individual scales and logarithmic transformation for statistical analysis.
• Experimental Design: Supports the use of analysis of variance (ANOVA) and other statistical methods to remove assessor bias and handle assessor-by-product interactions.

Applications

Magnitude estimation, as detailed in ASTM E1697, is suited for:

• Product Development and Quality Control: Comparing sensory intensities such as flavor, aroma, or texture among product variants.
• Sensory Benchmarking: Establishing and tracking product standards using trained sensory panels.
• Consumer and Market Research: Providing precise measurement of sensory differences that can inform marketing or reformulation strategies.
• Academic and Industrial Research: Applying Stevens’ Power Law and psychophysical scaling in sensory science studies.
• Centralized Sensory Testing: Ideal for trained panels in laboratory settings rather than home use or consumer intercept studies.
• Efficient Panel Training: With approximately one hour of training, panels of 15 to 20 individuals can provide reliable and reproducible results, making it cost-effective and efficient for routine sensory evaluation.

Related Standards

Several key standards and guidelines complement ASTM E1697, offering additional context and best practices for sensory evaluation:

• ASTM E253: Terminology Relating to Sensory Evaluation of Materials and Products.
• ASTM E1871: Guide for Serving Protocol for Sensory Evaluation of Foods and Beverages.
• ISO 6658: Sensory Analysis - Methodology - General Guidance.
• ISO 8586-1: Sensory Analysis - Methodology - General Guide for Selection, Training, and Monitoring of Assessors.
• ISO 11056: Sensory Analysis - Magnitude Estimation Method.
• ISO 4121: Sensory Analysis - Evaluation of Food Products Using Scales.
• ISO 8589: Sensory Analysis - General Guidance for the Design of Test Rooms.

Adhering to ASTM E1697-05(2020) enables organizations to generate precise, reproducible sensory data, supporting evidence-based decision making, product development, and compliance with internationally recognized standards in sensory analysis. By leveraging unipolar magnitude estimation, companies and researchers can advance the reliability and validity of their sensory evaluations, driving innovation and ensuring product quality.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1697 − 05 (Reapproved 2020)
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.
1. Scope E253Terminology Relating to Sensory Evaluation of Mate-
rials and Products
1.1 This test method describes a procedure for the applica-
E1871GuideforServingProtocolforSensoryEvaluationof
tion of unipolar magnitude estimation to the evaluation of the
Foods and Beverages
magnitude of sensory attributes. The test method covers
2.2 ASTM Publications:
procedures for the training of assessors to produce magnitude
Manual 26Sensory Testing Methods: 2nd Edition
estimations and statistical evaluation of the estimations.
STP758Guidelines for the Selection and Training of Sen-
1.2 Magnitude estimation is a psychophysical scaling tech-
sory Panel Members
nique in which assessors assign numeric values to the magni-
2.3 ISO Standards:
tude of an attribute. The only constraint placed upon the
ISO 11056:1999 Sensory Analysis—Methodology—
assessor is that the values assigned should conform to a ratio
Magnitude Estimation Method
principle.Forexample,iftheattributeseemstwiceasstrongin
ISO 4121:1987 Sensory Analysis—Methodology—
sample B when compared to sample A, sample B should
Evaluation of Food Products by Methods Using Scales
receive a value which is twice the value assigned to sampleA.
ISO/DIS5492:1990Sensory Analysis—Vocabulary (1)
1.3 The intensity of attributes such as pleasantness,
ISO6658:1985Sensory Analysis—Methodology—General
sweetness, saltiness or softness can be evaluated using magni-
Guidance
tude estimation.
ISO/DIS8586-1:1989Sensory Analysis—Methodology—
General Guide for Selection, Training and Monitoring
1.4 Magnitude estimation may provide advantages over
Subjects—Part 1: Qualifying Subjects (1)
other scaling methods, particularly when the number of asses-
ISO8589:1988Sensory Analysis—General Guidance for
sors and the time available for training are limited. With
the Design of Test Rooms
approximately1hof training, a panel of 15 to 20 naive
individuals can produce data of adequate precision and repro-
3. Terminology
ducibility. Any additional training that may be required to
3.1 Definitions:
ensure that the assessors can properly identify the attribute
3.1.1 For general definitions related to sensory evaluation,
being evaluated is beyond the scope of this test method.
refer to Terminology E253.
1.5 This international standard was developed in accor-
3.2 Definitions of Terms Specific to This Standard:
dance with internationally recognized principles on standard-
3.2.1 external modulus, n—number assigned by the panel
ization established in the Decision on Principles for the
leadertodescribetheintensityoftheexternalreferencesample
Development of International Standards, Guides and Recom-
or the first sample of the sample set. The external modulus is
mendations issued by the World Trade Organization Technical
sometimes referred to as a “fixed modulus” or just the
Barriers to Trade (TBT) Committee.
“modulus.” In this case the reference is said to be modulated.
2. Referenced Documents
3.2.2 external reference sample for magnitude estimation,
n—sample designated as the one to which all others are to be
2.1 ASTM Standards:
compared, or to which the first sample of a set is to be
compared,wheneachsubsequentsampleinthesetiscompared
ThistestmethodisunderthejurisdictionofASTMCommitteeE18onSensory
to the preceding sample. This sample is normally the first
Evaluation and is the direct responsibility of Subcommittee E18.03 on Sensory
sample to be presented.
Theory and Statistics.
Current edition approved Feb. 1, 2020. Published February 2020. Originally
ε1
approved in 1995. Last previous edition approved in 2012 as E1697–05(2012) .
DOI: 10.1520/E1697-05R20. Available from ASTM Headquarters, 100 Barr Harbor Drive, PO Box C700,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or West Conshohocken, PA 19428–29593.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Available from International Organization for Standardization (ISO), ISO
Standards volume information, refer to the standard’s Document Summary page on Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
the ASTM website. Geneva, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1697 − 05 (2020)
3.2.3 internal modulus, n—numberassignedbytheassessor 4.2 Individual judgments can be converted to a common
todescribetheintensityoftheexternalreferencesampleorthe scale by normalizing the data. Three normalizing methods can
first sample of the sample set. The internal modulus is be used: internal standard normalizing, external calibration
sometimes referred to as a “non-fixed modulus.” When an and,ifamodulusisnotused,nostandardnormalizing(method
internal modulus is used, the reference is sometimes said to be of averages). See 11.4 and Appendix X2 – Appendix X4.
unmodulated.
4.3 Results are averaged using geometric means. Analysis
ofvarianceorotherstatisticalanalysesmaybeperformedafter
3.2.4 internal reference sample for magnitude estimation,
n—sample present in the experimental set, which is presented the data have been converted to logarithms.
to the assessor as if it were a test sample. The value assigned
tothissample(s)canbeusedfornormalizingassessors’data.If 5. Significance and Use
an external reference is used, the internal reference(s) are
5.1 Magnitude estimation may be used to measure and
normally identical to it.
compare the intensities of attributes of a wide variety of
3.2.5 magnitude estimation, n—process of assigning values products.
to the intensities of an attribute of products in such a way that
5.2 Magnitude estimation provides a large degree of flex-
the ratios of the values assigned and the assessor’s perceptions
ibilityforboththeexperimenterandtheassessor.Oncetrained
of the attribute are the same.
in magnitude estimation, assessors are generally able to apply
3.2.6 normalizing, v—process of multiplying each asses- theirskilltoawidevarietyofsampletypesandattributes,with
minimal additional training.
sor’srawdataby,oraddingtothelogarithmofeachassessor’s
raw data, a value which brings all the data onto a common
5.3 Magnitudeestimationisnotassusceptibletoend-effects
scale. Also referred to as rescaling.
as interval scaling techniques.These can occur when assessors
are not familiar with the entire range of sensations being
3.2.7 Stevens’ Equation, n—also referred to as the Psycho-
physical Power Funtion: presented.Underthesecircumstances,assessorsmayassignan
early sample to a category which is too close to one end of the
n
R 5 KS (1)
scale. Subsequently, they may “run out of scale” and be forced
where:
to assign perceptually different samples to the same category.
R = the assessor’s response (the perceived intensity), Thisshouldnotoccurwithmagnitudeestimation,as,intheory,
K = aconstantthatreconcilestheunitsofmeasurementused there are an infinite number of categories.
for R and S,
5.4 Magnitude estimation is one frequently used technique
S = the stimulus (chemical concentration or physical force),
that permits the representation of data in terms of Stevens’
and
Power Law.
n = the exponent of the power function and the slope of the
5.5 The disadvantages of magnitude estimation arise pri-
regressioncurvefor Rand Swhentheyareexpressedin
marily from the requirements of the data analysis.
logarithmic units.
5.5.1 Permitting each assessor to choose a different numeri-
In practice, Stevens’ Equation is generally transformed to
cal scale may produce significant assessor effects. This disad-
logarithms, either common or natural:
vantagecanbeovercomeinanumberofways,asfollows.The
lnR 5 lnK1nlnS (2)
experimenter must choose the approach most appropriate for
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
scale,eitherbytrainingorbyuseofexternalreferencesamples
sample is twice as strong, it will be given a value of 100. If it
with assigned values (modulus).
is half as strong it will be given a value of 25. There are three
5.5.1.3 Finally, each assessor’s data can be brought to a
procedures that can be used.
common scale by one of a variety of normalizing methods.
4.1.1 Assessors are instructed to assign any value to de-
5.5.2 Logarithms must be applied before carrying out data
scribe the intensity of the first sample (external reference,
analysis. This becomes problematic if values are near
which may or may not be part of the sample set). Assessors
threshold, as a logarithm of zero cannot be taken (see 11.2.1).
then rate the intensity of the following samples in relation to
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.
E1697 − 05 (2020)
5.7 Thistestmethodisonlymeanttobeusedwithassessors 7.5 Assessorshaveatendencytouse“roundnumbers”such
who are specifically trained in magnitude estimation. Do not as 5, 10, 20, 25, and so forth. This should be pointed out
use this method with untrained assessors or untrained consum- explicitly during training. Assessors should be encouraged,
ers. “given permission,” to use all numbers. Assessors are also
influenced by the ratios mentioned in training. Therefore, care
6. Conditions of Testing
should be taken to mention a variety of different ratios, for
1 1
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 Figures—The figures are presented
selection and training of assessors are described in the stan-
singly, centered on an 8.5×11 in. sheet of white paper. The
dards for general methodology, such as ISO 6658, ISO/DIS
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 Results—After completing the full set of
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 7.8 If the assessors’ results are very different, review the
very useful for introducing assessors to the basic concepts of principles of the method again. If the panel leader judges that
magnitude estimation. A set of 18 figures composed of six a assessor cannot be trained in the method, the training should
circles,sixequilateraltriangles,andsixsquaresranginginsize be discontinued at this point and the assessor excused.
from approximately 2 to 200 cm has been used successfully
7.9 Once the panel has successfully completed the area
for training assessors (see Table 1).
estimation exercise, further training should be carried out with
the commodity or type of test substance to be used in the main
7.4 Prior to presenting the figures, the panel leader instructs
the candidate in the principles of the method. This instruction trial(s). This gives the assessor experience in applying magni-
tude estimation to attributes characterizing the test sample.
should include, but is not necessarily limited to the following
three points.
7.10 The panel leader may need to design exercises for
7.4.1 If the attribute is not present, the value 0 should be
training assessors to properly identify the attributes to be
assigned.
evaluated. The need for this will depend on the objectives and
7.4.2 There is no upper limit to the scale.
requirements of the test.
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. Number of Assessors Required
large.
8.1 As is true for other forms of scaling, the number of
assessorsnecessaryforagiventaskdependsonthecomplexity
of the task, how close together the various test samples are in
TABLE 1 Training Exercise Shapes
the attribute being evaluated, the amount of training the
NOTE 1—Two 11.1-cm squares are included as a measure of reproduc-
assessors have received, and the importance to be attached to
ibility.
the decision based on the test results (c.f. ISO 8586-1). Issues
Dimensions/Areas (cm/cm )
of statistical power need to be resolved based on the variance
Circles Triangles Squares
associated with a particular evaluation and the magnitude of
Radius Area Edge Area Edge Area
the differences that need to be detected.
1.4 6.2 2.2 2.1 3.2 10.2
2.5 19.6 4.1 7.3 4.2 17.6
9. Reference Samples
3.7 43.0 7.6 25.0 8.5 72.3
5.4 91.6 12.2 64.4 11.1 123.2
9.1 External References—The panel leader specifies to the
6.8 145.3 15.5 104.0 11.1 123.2
assessorsthatthereferencesamplehasavalueof,forexample,
8.3 216.4 19.2 159.6 14.2 201.6
30, 50, 100, or whatever seems appropriate to the panel leader.
E1697 − 05 (2020)
Theleaderinstructstheassessorstomakehisorhersubsequent critical factors. For example, when a project extends over
judgments relative to the value assigned. multiple sessions, it may not be possible to assemble exactly
the same group of assessors at each session. In other cases it
9.2 The reference should have an intensity close to the
may be necessary to combine samples from multiple projects
geometric mean for the whole panel. A reference that repre-
into a single session. If your design does not conform to
sents an extreme value of the attribute will distort the data due
standard experimental design, every effort should be made to
to a contrast effect and reduce the sensitivity of the method.
consult a statistician to develop an appropriate form of the
9.3 Magnitude estimation does not impose any specific
ANOVA model. If this is not an option, a less desirable but
restrictions on sample presentation. However, the external
workable solution may be to employ a one-wayANOVAusing
referencesample,ifused,ispresentedtotheassessorfirstwith
treatments as the only factor. Finally, when investigating the
the specification that the sample is to have a particular value.
dose-response relationship between some physical parameter
The value chosen should be between 30 and 100. In most
and a sensory attribute, regression analysis is appropriate.
instances, when the initial value is in this range, the assessor
11.1.1 It should be noted, that both normalizing and in-
will not need to use decimals in order to conform to the ratio
structing the assessors to rate each sample relative to the
principle. Some assessors find it more difficult to use decimals
immediately preceding sample cause certain theoretical prob-
andmostwillavoidusingthemunlessspecificallyinstructedto
lems in the statistical analysis. When these techniques are
do so.
employed,thestatisticalprobabilitiesarisingfromtheanalyses
should be regarded as approximate. The statistical approaches
10. Procedure—Assigning Magnitude Estimations
todealingwiththeseproblemsarebeyondthescopeofthistest
method.
10.1 Magnitude estimation imposes no special restrictions
on the method or order of sample presentation. As in all
11.2 Log Transformations—Present knowledge indicates
sensory experiments, the order of sample presentation should
that magnitude estimations conform to a log-normal
be randomized and balanced across all assessors.
distribution, and that more precise results are obtained when
analyses are carried out on logarithmically transformed data.
10.2 In the modalities of olfaction and gustation, the prob-
11.2.1 Dealing with Zeros—Since one cannot take the
lems of adaptation and fatigue must be carefully considered
logarithm of zero, any zero response causes a problem.
when encouraging or requiring repeated evaluations of previ-
Different investigators have used different approaches to deal-
ous samples. When only a limited number of samples can be
ing with zeros. It is recommended that the zero values should
evaluated, it may be necessary to sacrifice statistical rigor to
be replaced by very small values. The specific value chosen
the known limitations of the sensory systems.
should take into account the scale used by each assessor (for
10.3 Without an External Reference Sample—The assessor
example, half of the smallest value assigned by that assessor).
evaluates the first sample and assigns a magnitude estimate.
11.3 Product-Assessor Interactions:
The assessor is instructed to be careful not to assign a value
11.3.1 An external reference anchors the assessors to a
that is too small. It has generally been suggested that the first
common point on the scale. With experienced assessors, this
sample be assigned a value in the range of 30 to 100 (see 9.3).
often eliminates product-assessor interactions. (When this is
10.3.1 The assessor is then instructed to rate each sample
the case, the data require no special processing to remove this
relative to its immediately preceding sample or to the first
interaction.)
sample.
11.3.2 With assessors who have just been trained or when
10.4 With an External Reference Sample—The assessor is
no external reference is used, or both, product-assessor inter-
presented the reference sample and is informed of its assigned
actions may still occur. In this case, the methods discussed
valueorallowedtoassignavalueofhisown.Theassessornext
below can be used to reduce, or eliminate, this interaction.
evaluates the first coded sample and assigns it a value relative
11.4 Normalizing—Product-assessor interactions should
to the reference sample. All subsequent samples are rated
first be removed by normalizing. This significantly improves
relative to either the identified reference or to its immediately
the sensitivity of subsequent analyses. “Internal Standard
preceding sample.
Normalizing,” “No Standard Normalizing,” and “External
10.5 The procedure of rating each sample relative to its
Calibration”havebeenusedforthispurpose.Themostprecise
immediate predecessor can produce scale drift due to an
of these methods is “Internal Standard Normalizing.” It is
accumulation of errors. In addition, the random error associ-
recommended that this method be used wherever possible.
ated with each evaluation is no longer independent from the
11.4.1 Internal Standard Normalizing—This approach can
preceding evaluations (see Section 11).
beusedwhetherornotanexternalreferenceisused.Itrequires
that one or more unidentified internal reference samples be
11. Data Analysis
included in the test set.
11.1 An analysis of variance (ANOVA), which explicitly 11.4.1.1 When replicate internal reference samples have
accounts fo
...