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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 triangle test, the duo-trio test is statistically less efficient, but easier to perform by the assessors. For details on how the duo-trio test compares to other three-sample tests, see Refs (1-4).2

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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.8 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.

5.1 The test method is effective for the following test objectives:

5.2 The test method itself does not change whether the purpose of the duo-trio test is to determine that two products are perceivably different versus that the products are not perceivably different. Only the selected values of p_d, α, and β change. If the objective of the test is to determine if there is a perceivable difference between two products, then the value selected for α is typically smaller than the value selected for β. If the objective is to determine if the two products are sufficiently similar to be used interchangeably, then the value selected for β is typically smaller than the value selected for α and the value of p_d is selected to define “sufficiently similar.”

5.3 The test method may change based on the test objective or the assessors’ familiarity with the product. The balanced-reference technique (see 9.1.1) typically is used when neither product is more familiar than the other. The constant-reference technique (see 9.1.2) frequently is used when one product is a control/current product or is familiar to the assessors.