This is logically related to historical psychophysical methods such as the constant stimulus method. The most common forms of the discrimination procedure are the triangle test and the duo-trio procedure. The triangle test is a three-alternative test in which one sample is different from the other two. Chance performance is one third, and performance in a group above that level provides evidence for a perceivable difference. This differs from traditional forced-choice procedures in which subjects would be directed to choose the strongest or weakest stimulus.
Foods are necessarily multivariate.
In the duo-trio test, a sample designated as a standard or control sample is presented for inspection. Then two samples are presented, and the participant is asked which of the two matches the control. Participants in these tests should be screened for minimal acuity in discriminating differences in the products or sensory modalities to be tested. Since the tests are often used as a first step in a sequence of tests, there is little attempt to make the selection of participants be representative of consumers as a whole. Rather, discriminative ability is key.