ASTM E2262-03(2009)
(Practice)Standard Practice for Estimating Thurstonian Discriminal Distances
Standard Practice for Estimating Thurstonian Discriminal Distances
SIGNIFICANCE AND USE
Under the assumptions of the model, the Thurstonian model approach to measuring the perceived difference between two samples (whether overall or for a specific attribute) is independent of the sensory method used to collect the data. Converting results obtained from different test methods to d' values permits the assessment of relative differences among samples without requiring that the samples be compared to each other directly or that the same test methods be used for all pairs of samples.
Thurstonian scaling has been applied to:
Creating a historical database to track differences between production and reference samples over periods in which different test methods were used to measure the difference,
Comparing the relative sensitivities of different user groups and consumer segments,
Comparing trained panels that use different measuring techniques,
Comparing the relative sensitivities of consumers versus trained panels,
Comparing different methods of consumer testing (for example, CLT versus HUT, preference versus hedonic scales, etc.), and
Comparing different discrimination test methods.
SCOPE
1.1 This practice describes procedures to estimate Thurstonian discriminal distances (that is, d' values) from data obtained on two samples. Procedures are presented for four forced-choice methods (that is, the triangle, the duo-trio, the 3-alternative-forced-choice (or 3-AFC) and the 2-AFC (also called the directional difference test)), the A/Not-A method, the Same-Different method and for data obtained from ordered category scales. Procedures for estimating the variance of d' are also presented. Thus, confidence intervals and statistical tests can be calculated for d'.
1.2 The procedures in this document pertain only to the unidimensional, equal-variance model. Other, more complicated Thurstonian models, involving multiple dimensions and unequal variances exist but are not addressed in this standard. The procedure for forced-choice methods is limited to dichotomous responses. The procedure for the A/Not-A method assumes equal sample sizes for the two samples. The procedure for the Same-Different method assumes equal sample sizes for the matched and unmatched pairs of samples. For all methods, only unreplicated tests are considered. (Tests in which each assessor performs multiple (that is, replicated) evaluations require different analyses.)
1.3 Thurstonian scaling is a method for measuring the perceptual difference between two samples based on a probabilistic model for categorical choice decision making. The magnitude of the perceived difference, δ, can be estimated from the assessors' categorical choices using the methods described in this practice (See Appendix X3 for a more detailed description of Thurstonian scaling).
1.4 In theory, the Thurstonian δ does not depend on the method used to measure the difference between two samples. As such, δ provides a common scale of measure for comparing samples measured under a variety of test conditions. For example, Thurstonian scaling can be used to compare products measured under different test conditions, to compare panels (trained, consumer or both) that have evaluated the same samples (using the same or different test methods) and to compare test methods on their ability to discriminate samples that exhibit a fixed sensory difference.
1.5 This standard may involve hazardous materials, operations and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: E2262 − 03(Reapproved 2009)
Standard Practice for
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Estimating Thurstonian Discriminal Distances
This standard is issued under the fixed designation E2262; 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 (trained, consumer or both) that have evaluated the same
samples (using the same or different test methods) and to
1.1 This practice describes procedures to estimate Thursto-
compare test methods on their ability to discriminate samples
nian discriminal distances (that is, d’ values) from data
that exhibit a fixed sensory difference.
obtained on two samples. Procedures are presented for four
1.5 This standard may involve hazardous materials, opera-
forced-choice methods (that is, the triangle, the duo-trio, the
tions and equipment. This standard does not purport to address
3-alternative-forced-choice (or 3-AFC) and the 2-AFC (also
all of the safety concerns, if any, associated with its use. It is
calledthedirectionaldifferencetest)),theA/Not-Amethod,the
the responsibility of the user of this standard to establish
Same-Different method and for data obtained from ordered
appropriate safety and health practices and determine the
category scales. Procedures for estimating the variance of d’
applicability of regulatory limitations prior to use.
are also presented. Thus, confidence intervals and statistical
tests can be calculated for d’.
2. Referenced Documents
1.2 The procedures in this document pertain only to the
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2.1 ASTM Standards:
unidimensional, equal-variance model. Other, more compli-
E253Terminology Relating to Sensory Evaluation of Mate-
cated Thurstonian models, involving multiple dimensions and
rials and Products
unequal variances exist but are not addressed in this standard.
E456Terminology Relating to Quality and Statistics
Theprocedureforforced-choicemethodsislimitedtodichoto-
E460Practice for Determining Effect of Packaging on Food
mous responses. The procedure for the A/Not-A method
and Beverage Products During Storage
assumesequalsamplesizesforthetwosamples.Theprocedure
E679Practice for Determination of Odor and Taste Thresh-
for the Same-Different method assumes equal sample sizes for
olds By a Forced-ChoiceAscending Concentration Series
the matched and unmatched pairs of samples. For all methods,
Method of Limits
only unreplicated tests are considered. (Tests in which each
E1432Practice for Defining and Calculating Individual and
assessor performs multiple (that is, replicated) evaluations
require different analyses.) Group SensoryThresholds from Forced-Choice Data Sets
of Intermediate Size
1.3 Thurstonian scaling is a method for measuring the
E1593GuideforAssessingtheEfficacyofAirCareProducts
perceptual difference between two samples based on a proba-
in Reducing Sensorly Perceived Indoor Air Malodor
bilistic model for categorical choice decision making. The
Intensity
magnitude of the perceived difference, δ, can be estimated
E1627Practice for Sensory Evaluation of Edible Oils and
from the assessors’ categorical choices using the methods
Fats
describedinthispractice(SeeAppendixX3foramoredetailed
E1697Test Method for Unipolar Magnitude Estimation of
description of Thurstonian scaling).
Sensory Attributes
1.4 In theory, the Thurstonian δ does not depend on the
E1810Practice for Evaluating Effects of Contaminants on
method used to measure the difference between two samples.
Odor and Taste of Exposed Fish
Assuch, δprovidesacommonscaleofmeasureforcomparing
E1879Guide for Sensory Evaluation of Beverages Contain-
samples measured under a variety of test conditions. For
ing Alcohol
example,Thurstonian scaling can be used to compare products
E1885Test Method for Sensory Analysis—Triangle Test
measured under different test conditions, to compare panels
E1958Guide for Sensory Claim Substantiation
E2049 Guide for Quantitative Attribute Evaluation of
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This practice is under the jurisdiction of ASTM Committee E18 on Sensory
Evaluation and is the direct responsibility of Subcommittee E18.03 on Sensory
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Theory and Statistics. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Sept. 1, 2009. Published March 2010. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2003. Last previous edition approved in 2003 as E2262–03. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2262-03R09. the ASTM website.
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