1.1 本测试方法涵盖了使用两种替代强制选择任务比较两种产品的程序。 1.2 这种方法有时被称为配对比较测试或2-AFC（替代强制选择）测试。 1.3 方向差异测试确定两个样本之间特定感官属性的感知强度是否存在差异。 1.4 方向差异测试仅限于应用于特定的感官属性，并不直接确定该特定属性的差异大小。评估员必须能够识别和理解指定的属性。 指定属性中没有差异并不意味着不存在总体差异。 1.5 此测试方法不涉及偏好。 1.6 方向差异测试对评估人员来说是一项简单的任务，在感觉疲劳或遗留问题时使用。方向差异测试的疲劳、遗留或适应程度与三角形或二对三测试等多样本测试不同。有关各种差异测试之间比较的详细信息，请参阅Ennis ( 1. ) 麦克雷 ( 2. ) 还有奥马霍尼和奥德伯特 ( 3. ) . 2. 1.7 本文件所述的测试程序包括向评估员提交一对样品。 1.8 本标准并不旨在解决与其使用相关的所有安全问题（如果有的话）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践，并确定监管限制的适用性。 1.9 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 =====意义和用途====== 5.1 方向差异测试以给定的置信水平确定两个样本之间指定属性的强度是否存在可感知的差异，例如，当成分、工艺、包装、处理或储存发生变化时。 5.2 当评估具有不易指定、不易理解或事先未知的感官特征的产品时，方向差测试是不合适的。应使用其他差异测试方法，如相同的不同测试。 5.3 特定属性没有显著差异的结果并不能保证两个样本在其他属性或特征上没有差异，也不能表明两个样本的属性是相同的。 这可能只是表明差异程度太低，无法用灵敏度（α、β和P 最大值 )被选为测试对象。 5.3.1 该方法本身不会改变测试的目的是确定两个样本是否存在可感知的差异，还是两个样本没有可感知的不同。只有选定的P值 最大值 α和β发生变化。如果测试的目的是确定两个样本是否存在可感知的差异，那么为α选择的值通常小于为β选择的值。如果目的是确定是否不存在可感知的差异，那么为β选择的值通常小于为α和P选择的值 最大值 需要明确说明。

1.1 This test method covers a procedure for comparing two products using a two-alternative forced-choice task. 1.2 This method is sometimes referred to as a paired comparison test or as a 2-AFC (alternative forced choice) test. 1.3 A directional difference test determines whether a difference exists in the perceived intensity of a specified sensory attribute between two samples. 1.4 Directional difference testing is limited in its application to a specified sensory attribute and does not directly determine the magnitude of the difference for that specific attribute. Assessors must be able to recognize and understand the specified attribute. A lack of difference in the specified attribute does not imply that no overall difference exists. 1.5 This test method does not address preference. 1.6 A directional difference test is a simple task for assessors, and is used when sensory fatigue or carryover is a concern. The directional difference test does not exhibit the same level of fatigue, carryover, or adaptation as multiple sample tests such as triangle or duo-trio tests. For detail on comparisons among the various difference tests, see Ennis ( 1 ) , MacRae ( 2 ) , and O'Mahony and Odbert ( 3 ) . 2 1.7 The procedure of the test described in this document consists of presenting a single pair of samples to the assessors. 1.8 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. 1.9 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. ====== Significance And Use ====== 5.1 The directional difference test determines with a given confidence level whether or not there is a perceivable difference in the intensity of a specified attribute between two samples, for example, when a change is made in an ingredient, a process, packaging, handling, or storage. 5.2 The directional difference test is inappropriate when evaluating products with sensory characteristics that are not easily specified, not commonly understood, or not known in advance. Other difference test methods such as the same-different test should be used. 5.3 A result of no significant difference in a specific attribute does not ensure that there are no differences between the two samples in other attributes or characteristics, nor does it indicate that the attribute is the same for both samples. It may merely indicate that the degree of difference is too low to be detected with the sensitivity (α, β, and P max ) chosen for the test. 5.3.1 The method itself does not change whether the purpose of the test is to determine that two samples are perceivably different versus that the samples are not perceivably different. Only the selected values of P max , α, and β change. If the objective of the test is to determine if the two samples are perceivably different, then the value selected for α is typically smaller than the value selected for β. If the objective is to determine if no perceivable difference exists, then the value selected for β is typically smaller than the value selected for α and the value of P max needs to be stated explicitly.