1. Duo, trio and tetrad methods: Is there a difference?
H L de Kock
Institute for Food, Nutrition & Wellbeign

2. unwanted change in the product
Balance the risk
cost saving
unwanted change in the product
Operations has identified a process change that offers the potential for substantial cost savings.
Quality Control is concerned that the change may be noticeable to consumers and would represent a risk to business.
To determine if a sensory difference can be perceived between products made using the two processes.
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3. Product with cost saving B
Standard A
Product with cost saving B
We want to make a change to our product but we do not want consumers to notice.
Will they notice?
Difference
Similarity
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4. What are the options? Paired comparison: Same-different
Triangle test/ 3 Alternative Force Choice
Duo-trio test
Tetrad
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5. Paired comparison: Same-different
You have received two tomatoes. Taste the tomatoes in the order presented and tick a box to indicate whether the tomatoes are the same or different.
348
912
SAME
DIFFERENT
We want to make a change to our product but we do not want consumers to notice.
Will they notice?
Difference
Similarity
7 May 2019

6. Same/Different A B AB BA AA BB
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7. Triangle test/3 AFC
You have received three tomatoes. Two of the tomatoes are the same and one is different. Taste the tomatoes in the order presented and circle the code of the tomato that is different from the other two.
348
912
We want to make a change to our product but we do not want consumers to notice.
Will they notice?
Difference
Similarity
556
7 May 2019

8. Triangle/3 AFC
AAB
BBA
ABA
ABB
BAB
BAA
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9. Duo-trio
You have received three tomatoes. One of the tomatoes is a reference sample (R). Taste R first, and then taste the two coded tomatoes in the order presented. Circle the code of the tomato that is most similar to R. R
912
We want to make a change to our product but we do not want consumers to notice.
Will they notice?
Difference
Similarity
556
7 May 2019

10. Duo-trio RA AB BA
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11. Duo-trio RA AB BA RB
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12. Group the tomatoes in two groups of two based on similarity.
Tetrad
You have received four tomatoes. There are two groups of two similar tomatoes. Taste the tomatoes in the order presented.
Group the tomatoes in two groups of two based on similarity.
348
912
Group
720
556
We want to make a change to our product but we do not want consumers to notice.
Will they notice?
Difference
Similarity
7 May 2019

13. Tetrad
AABB
BBAA
ABAB
ABBA
BABA
BAAB
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14. The tetrad test is more efficient statistically than the triangle test or the duo-trio test.
Tetrad > Triangle > Paired/Duo trio
Practically,
four vs three vs two samples
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15. Tetrad - steps Clearly define the test objective.
Choose the number of assessors based on the sensitivity desired for the test.
The sensitivity of the test is a function of three values:
the risk of declaring the samples different when they are not (i.e, α-risk)
the risk of not declaring the samples different when they are (i.e, β-risk).
the maximum allowable sensory difference, δ
Acceptable values of α and β vary depending on the test objective and should be determined before the test .
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16. Prior to conducting the test, select values for α, β, and δ
0 to 5 % (0.10 to 0.05) indicates “slight” evidence
5 to 1 % (0.05 to 0.01) indicates “moderate” evidence
1 to 0.1 % (0.01 to 0.001) indicates “strong” evidence that a difference was apparent β
1 to 0.1 % (0.01 to 0.001) indicates “strong” evidence that a difference was NOT apparent δ
δ < 0.5 represent small values;
0.5 < δ < 1 represent medium sized values;
δ > 1 represent large values
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17. Meaningful sensory difference for company
Risk for Operations
Meaningful sensory difference for company
The company’s action standard for a meaningful sensory difference has been set at δ = The analyst is equally concerned about failing to take advantage of the cost savings and unintentionally introducing a perceptible change in the product. Therefore, the analyst sets both the α-risk and the β-risk at 0.10.
Risk for QC
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18. n = 36 respondents for the test in order to present each of the six possible serving orders of the samples equally often.
72 X A samples, 72 X B samples
36 scoresheets.
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19. Results
A total of 15 of the 36 respondents correctly grouped the samples into two groups of two.
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20. Analysis and interpretation of results
From Table, the number of correct responses for significance at the 10 % risk level with 36 respondents is 17.
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21. Conclusion
Because 15 correct responses is less than the critical number, 17,
Conclude with 90 % confidence that any difference that exists between A and B is less than δ = 1.25, so the new process can be implemented.
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22. Take home message Sensitivity required = n number of assessors
Increasing the number of assessors increases the likelihood of detecting small values of δ.
larger numbers of assessors when trying to demonstrate that products are similar compared to when testing for a difference = 40 to 50
Practical considerations
Time available
Number of assessor available
Quantity of product available
Resources incl. budget
ASTM
7 May 2019