ASTM E1885-97(2003)
(Test Method)Standard Test Method for Sensory Analysis—Triangle Test
Standard Test Method for Sensory Analysis—Triangle Test
SCOPE
1.1 This test method covers a procedure for determining whether a perceptible sensory difference exists between samples of two products.
1.2 This test method applies whether a difference may exist in a single sensory attribute or in several.
1.3 This test method is applicable when the nature of the difference between the samples is unknown. It does not determine the size or the direction of the difference. The attribute(s) responsible for the difference are not identified.
1.4 Compared to the duo-trio test, the triangle test can achieve an equivalent level of statistical significance with fewer assessors. For details on how the triangle test compares to other three-sample tests, see Refs (1), (2), (3) and (4).
1.5 This test method is applicable only if the products are homogeneous. If two samples of the same product can often be distinguished, then another method, for example, descriptive analysis, may be more appropriate.
1.6 This test method is applicable only when the products do not cause excessive sensory fatigue, carryover or adaptation.
1.7 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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Designation: E 1885 – 97 (Reapproved 2003)
Standard Test Method for
Sensory Analysis — Triangle Test
This standard is issued under the fixed designation E 1885; 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 4120 Sensory Analysis – Methodology – Triangular
Test
1.1 This test method covers a procedure for determining
whether a perceptible sensory difference exists between
3. Terminology
samples of two products.
3.1 Definitions–For definition of terms relating to sensory
1.2 This test method applies whether a difference may exist
analysis, see Terminology E 253, and for terms relating to
in a single sensory attribute or in several.
statistics, see Terminology E 456.
1.3 This test method is applicable when the nature of the
3.2 Definitions of Terms Specific to This Standard:
difference between the samples is unknown. It does not
3.2.1 a (alpha) risk—the probability of concluding that a
determine the size or the direction of the difference. The
perceptible difference exists when, in reality, one does not.
attribute(s) responsible for the difference are not identified.
(Also known as Type I Error or significance level.)
1.4 Compared to the duo-trio test, the triangle test can
3.2.2 b (beta) risk—the probability of concluding that no
achieve an equivalent level of statistical significance with
perceptible difference exists when, in reality, one does. (Also
fewer assessors. For details on how the triangle test compares
2 known as Type II Error.)
to other three-sample tests, see Refs (1), (2), (3) and (4).
3.2.3 p —the probability of a correct response.
c
1.5 This test method is applicable only if the products are
3.2.4 p (proportion of discriminators)—the proportion of
d
homogeneous. If two samples of the same product can often be
the population represented by the assessors that can distinguish
distinguished, then another method, for example, descriptive
between the two products.
analysis, may be more appropriate.
3.2.5 product—the material to be evaluated.
1.6 This test method is applicable only when the products
3.2.6 sample—the unit of product prepared, presented, and
do not cause excessive sensory fatigue, carryover or adapta-
evaluated in the test.
tion.
3.2.7 sensitivity—a general term used to summarize the
1.7 This standard does not purport to address all of the
performance characteristics of the test. The sensitivity of the
safety concerns, if any, associated with its use. It is the
test is rigorously defined, in statistical terms, by the values
responsibility of the user of this standard to establish appro-
selected for a, b, and p .
d
priate safety and health practices and determine the applica-
3.3 triad—the three uniquely coded samples given to an
bility of regulatory limitations prior to use.
assessor in the triangle test; two samples are alike (that is, of
2. Referenced Documents one product) and one is different (that is, of the other product).
2.1 ASTM Standards:
4. Summary of Test Method
E 253 Terminology Relating to Sensory Evaluation of Ma-
3 4.1 Clearly define the test objective in writing.
terials and Products
4 4.2 Choose the number of assessors based on the level of
E 456 Terminology for Relating to Quality and Statistics
sensitivity desired for the test. The sensitivity of the test is, in
E 1871 Practice for Serving Protocol for Sensory Evalua-
3 part, a function of two competing risks: the risk of declaring
tion of Foods and Beverages
the samples different when they are not (that is, a-risk) and the
2.2 ISO Standard:
risk of not declaring the samples different when they are (that
is, b-risk). Acceptable values of a and b vary depending on the
test objective and should be determined before the test (see
This test method is under the jurisdiction of ASTM Committee E18 on Sensory
Appendix X3).
Evaluation of Materials and Products and is the direct responsibility of Subcom-
4.3 Assessors receive a triad and are informed that two of
mittee E18.04 on Fundamentals of Sensory.
the samples are alike and that one is different. The assessors
Current edition approved April 10, 2003. Published June 2003. Originally
approved in 1997. Last previous edition approved in 1997 as E 1885 – 97.
The boldface numbers given in parentheses refer to a list of references at the
end of the text.
3 5
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E 1885 – 97 (2003)
report which they believe to be the different, or “odd,” sample, 7.5 Pooling multiple evaluations by the same assessor is not
even if the selection is based only on a guess. recommended because results are less representative of the
4.4 Results are tallied and significance determined by ref- population and the risk of incorrect conclusion is greater.
erence to a statistical table.
8. Number of Assessors
5. Significance and Use
8.1 Choose the number of assessors to yield the level of
5.1 This test method is effective for the following test
sensitivity called for by the test objectives. The sensitivity of
objectives:
the test is a function of three values: the a-risk, and the b-risk,
5.1.1 To determine whether a perceivable difference results
and the maximum allowable proportion of distinguishers, p .
d
or a perceivable difference does not result, for example, when
8.2 Prior to conducting the test, select values for a, b and
a change is made in ingredients, processing, packaging, han-
p . The following can be considered as general guidelines.
d
dling or storage; or
8.2.1 For a-risk: A statistically significant result at:
5.1.2 To select, train and monitor assessors.
8.2.1.1 10 to 5 % (0.10 to 0.05) indicates “slight” evidence
5.2 This test method itself does not change whether the
that a difference was apparent;
purpose of the triangle test is to determine that two products are
8.2.1.2 5 to 1 % (0.05 to 0.01) indicates “moderate” evi-
perceivably different versus that the products are not perceiv-
dence that a difference was apparent;
ably different. Only the selected values of p , a, and b change.
d
8.2.1.3 1 to 0.1 % (0.01 to 0.001) indicates “strong” evi-
If the objective of the test is to determine if there is a
dence that a difference was apparent; and
perceivable difference between two products, then the value
8.2.1.4 Below 0.1 % (<0.001) indicates “very strong” evi-
selected for a is typically smaller than the value selected for b.
dence that a difference was apparent.
If the objective is to determine if the two products are
8.2.2 For b–risk: The strength of the evidence that a
sufficiently similar to be used interchangeably, then the value
difference was not apparent is assessed using the same criteria
selected for b is typically smaller than the value selected for a
as above (substituting “was not apparent” for “was apparent”).
and the value of p is selected to define “sufficiently similar.”
d
8.2.3 For p : the maximum allowable proportion of distin-
d
guishers, p , falls into three ranges:
d
6. Apparatus
8.2.3.1 p < 25 % represent small values;
d
6.1 Carry out the test under conditions that prevent contact
8.2.3.2 25 % < p < 35 % represent medium sized values;
d
between assessors until the evaluations have been completed
and
for example, booths that comply with STP 913 (5).
8.2.3.3 p > 35 % represent large values.
d
6.2 Sample preparation and serving sizes should comply
8.3 Having defined the required level of sensitivity for the
with Practice E 1871. See Refs (6) or (7).
test using 8.2, use Table A1.1 to determine the number of
assessors necessary. Enter Table A1.1 in the section corre-
7. Assessors
sponding to the selected value of p and the column corre-
d
7.1 All assessors must be familiar with the mechanics of the
sponding to the selected value of b. The minimum required
triangle test (the format, the task, and the procedure of
number of assessors is found in the row corresponding to the
evaluation). Experience and familiarity with the product and
selected value of a. Alternatively, Table A1.1 can be used to
test method may increase the sensitivity of an assessor and may
develop a set of values for p , a and b that provide acceptable
d
therefore increase the likelihood of finding a significant differ-
sensitivity while maintaining the number of assessors within
ence. Monitoring the performance of assessors over time may
practical limits. The approach is presented in detail in Ref (9).
be useful for increased sensitivity.
8.4 Often in practice, the number of assessors is determined
7.2 Choose assessors in accordance with test objectives. For
by material conditions (for example, duration of the experi-
example, to project results to a general consumer population,
ment, number of available assessors, quantity of product).
assessors with unknown sensitivity might be selected. To
However, increasing the number of assessors increases the
increase protection of product quality, assessors with demon-
likelihood of detecting small proportions of distinguishers.
strated acuity should be selected.
Thus, one should expect to use larger numbers of assessors
7.3 The decision to use trained or untrained assessors should
when trying to demonstrate that products are similar compared
be addressed prior to testing. Training may include a prelimi-
to when one is trying to prove they are different. Often 18 to 36
nary presentation on the nature of the samples and the problem
assessors are used when testing for a difference. For compa-
concerned. If the test concerns the detection of particular taint,
rable sensitivity when testing for similarity, 42 to 78 assessors
consider the inclusion of samples during training that demon-
are needed.
strate its presence and absence. Such demonstration will
increase the panel’s acuity for the taint but may detract from
other differences. See STP 758 for details (8). Allow adequate
time between the exposure to the training samples and the
In this test method, the probability of a correct response, p is modeled as p =
d c
a/b a/b
1 p + (1/3) (1-p ), where p is the proportion of the entire population of
actual triangle test to avoid carryover. d d d
assessors who can distinguish between the two products. It is a strictly statistical
7.4 During the test sessions, avoid giving information about
“guessing model” of the assessor’s behavior. It is not a psychometric model of the
product identity, expected treatment effects, or individual
assessor’s decision process, such as the Thurstone-Ura model that could also be
performance until all testing is complete. applied in discrimination testing.
E 1885 – 97 (2003)
9. Procedure assessor who detects no difference between the samples should
be instructed to randomly select one of the samples as being the
9.1 Prepare worksheets and scoresheets (see Appendix X1-
odd one and can indicate that the selection was only a guess in
Appendix X3) in advance of the test so as to utilize an equal
the comments section of the scoresheet.
number of the six possible sequences of two products, A and B.
Distribute these at random in groups of six among the
10. Analysis and Interpretation of Results
panelists. The six sequences are:
ABB AAB ABA 10.1 Use Table A1.2 to analyze the data obtained from a
BAA BBA BAB
triangle test. The actual number of assessors can be greater than
the minimum value given in Table A1.1. If the number of
9.2 Sometimes the final number of assessors does not end
correct responses is greater than or equal to the number given
up as a multiple of six. For example, if a test was planned for
in Table A1.2, conclude that a perceptible difference exists
36 assessors and only 34 actually participated, there would be
between the samples. If the number of correct responses is less
five complete series of the six sequences and one incomplete
than the number given in Table A1.2, conclude that the samples
set of four in which two of the six triads were randomly
are sufficiently similar. Again, the conclusions are based on the
dropped.
risks accepted when the level of sensitivity (that is, p , a, and
9.3 It is critical to the validity of the test that assessors
d
b) was selected in determining the number of assessors.
cannot identify the samples from the way in which they are
10.2 If desired, calculate a confidence interval on the
presented. For example, in a test evaluating flavor differences,
proportion of the population that can distinguish the samples.
one should avoid any subtle differences in temperature or
This method is described in Appendix X4.
appearance caused by factors such as the time sequence of
preparation. It may be possible to mask color differences using
light filters, subdued illumination, or colored serving contain- 11. Report
ers. Code the serving containers containing the samples in a
11.1 Report the test objective, the results, and the conclu-
uniform manner, preferably using three-digit numbers, chosen
sions. The following additional information is recommended:
at random for each test. Prepare samples out of sight and in an
11.1.1 The purpose of the test and the nature of the
identical manner: same apparatus, same serving containers, and
treatment studied;
same quantities of products (see ASTM Serving Protocols).
11.1.2 Full Identification of the Samples—Origin, method
9.4 Present each triad simultaneously if possible, following
of preparation, quantity, shape, storage prior to testing, serving
the same spatial arrangement for each assessor (on a line to be
size, temperature. (Sample information should communicate
sampled always from left to right, in a triangular array, etc.)
that all storage handling, and preparation was done in such a
Within the triad, assessors are typically allowed to make
way as to yield samples that differ only due to the variable of
repeated evaluations of each sample as desired. If the condi-
interest, if at all);
tions of the test require the prevention of repeat evaluations for
11.1.3 The number of assessors, the number of correct
example, if samples are bulky, leave an aftertaste, or show
selections, and the result of the statistical evaluation;
slight differences in appearance that cannot be masked, present
11.1.4 Assessors—Age, gender, experience in sensory test-
the samples sequentially and do not allow repeated evaluations.
ing, with the product, with the sam
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