This international Standard describes a procedure for detemining whether there exists a perceptible sensory difference or similarity between samples of two products concerning the intensity of a sensory attribute.This test is sometimes also referred to as a directional difference test or a 2-AFC test(Alternative Forced Choice).
NOTE The paired comparison test is the simplest existing classification test since it concerns lnly two samples.
The method is applicable whether a difference exists in a single sensory attribute or in several,which means that it enables detemination of wheter there exists a perceptible difference concerning a given attribure,and the specification of the direction of difference ,but it does not give any indication of the extent of that difference. The absence of difference for the attribute under study does not signify that there does not exist any difference between the two products.
This method is only applicable if the products are relatively homogeneous.
The method is effective
a) for determining
- whether a perceptible difference exists (paired idfference test),or
- whether no perceptible difference exists (paired similarity test)when,for example,modifications are made to ingredients,processing,packaging,handing or storage operation,or
b) for selecting,training and monitoring assessors.
It is necessary to know,prior to carrying out the test,whether the test is a one-sided test (the test supervisor knows a priori the direction of the difference,and the alternative hypothesis corresponds to the existence of a difference in the expected direction)or a two-sided testsupervisor does not have any a priori knowledge concerning the direction of the defference,and the alternatice hypothesis correspinds to the existence of a difference in one directon or the other).
The paired test can also be used in order to compare two products in terms of preference.The different cases of use of the paired test are summarized in Figure1.