This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages) This article may require cleanup to meet Wikipedia's quality standards. The specific problem is: too many subsections. Please help improve this article if you can. (June 2012) (Learn how and when to remove this template message) This article's lead section may be too short to adequately summarize the key points. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. (June 2012) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: "Discrimination testing" – news · newspapers · books · scholar · JSTOR (December 2009) (Learn how and when to remove this template message) (Learn how and when to remove this template message)

Discrimination testing is a technique employed in sensory analysis to determine whether there is a detectable difference among two or more products. The test uses a group of assessors (panellists) with a degree of training appropriate to the complexity of the test to discriminate from one product to another through one of a variety of experimental designs. Though useful, these tests typically do not quantify or describe any differences, requiring a more specifically trained panel under different study design to describe differences and assess significance of the difference.

Statistical basis

The statistical principle behind any discrimination test should be to reject a null hypothesis (H0) that states there is no detectable difference between two (or more) products. If there is sufficient evidence to reject H0 in favor of the alternative hypothesis, HA: There is a detectable difference, then a difference can be recorded. However, failure to reject H0 should not be assumed to be sufficient evidence to accept it. H0 is formulated on the premise that all of the assessors guessed when they made their response. The statistical test chosen should give a probability value that the result was arrived at through pure guesswork. If this probability is sufficiently low (usually below 0.05 or 5%) then H0 can be rejected in favor of HA.

Tests used to decide whether or not to reject H0 include binomial, χ2 (Chi-squared), t-test etc.

Types of test

A number of tests can be classified as discrimination tests. If it's designed to detect a difference then it's a discrimination test. The type of test determines the number of samples presented to each member of the panel and also the question(s) they are asked to respond to.

Schematically, these tests may be described as follows; A & B are used for knowns, X and Y are used for different unknowns, while (AB) means that the order of presentation is unknown:

Paired comparison
XY or (AB) – two unknown samples, known to be different, test is which satisfies some criterion (X or Y); unlike the others this is not an equality test.
Duo-trio
AXY – one known, two unknown, test is which unknown is the known (X = A or Y = A)
Triangle
(XXY) – three unknowns, test is which is odd one out (Y = 1, Y = 2, or Y = 3).
ABX
ABX – two knowns, one unknown, test is which of the knowns the unknown is (X = A or X = B).
Duo-trio in constant reference mode
(AB)X – three unknowns, where it is stated that the first two are different, but which is which is not identified, test is which of the first two the third is (X = 1 or X = 2).

Paired comparison

In this type of test the assessors are presented with two products and are asked to state which product fulfils a certain condition. This condition will usually be some attribute such as sweetness, sourness, intensity of flavor, etc. The probability for each assessor arriving at a correct response by guessing is

Advantages

Minimum number of samples required. Most straightforward approach when the question is 'Which sample is more ____?"

Disadvantages

Need to know in advance the attribute that is likely to change. Not statistically powerful with large panel sizes required to obtain sufficient confidence.[citation needed]

Duo-trio

The assessors are presented with three products, one of which is identified as the control. Of the other two, one is identical to the control, the other is the test product. The assessors are asked to state which product more closely resembles the control.

The probability for each assessor arriving at a correct response by guessing is

Advantages

Quick to set up and execute. No need to have prior knowledge of nature of difference.

Disadvantages

Not statistically powerful therefore relatively large panel sizes required to obtain sufficient confidence.

Triangle

The assessors are presented with three products, two of which are identical and the other one different. The assessors are asked to state which product they believe is the odd one out.[1]

The probability for each assessor arriving at a correct response by guessing is

Advantages

Can be quick to execute and offers greater power than paired comparison or duo-trio.

Disadvantages

Error might occur:

There are many other errors which can occur but the above are the main possible errors. It is evident from the above information that randomization, control and professional conduct of the experiment are essential for obtaining the most accurate results.

Important

Used to assist research and development in formulating and reformulating products. Using the triangle design to determine if a particular ingredient change, or a change in processing, creates a detectable difference in the final product. Triangle taste testing is also used in quality control to determine if a particular production run (or production from different factories) meets the quality-control standard (i.e., is not different from the product standard in a triangle taste test using discriminators).

ABX

Further information: ABX test

The assessors are presented with three products, two of which are identified as reference A and alternative B, the third is unknown X, and identical to either A or B. The assessors are asked to state which of A and B the unknown is; the test may also be described as "matching-to-sample", or "duo-trio in balanced reference mode" (both knowns are presented as reference, rather than only one).

ABX testing is widely used in comparison of audio compression algorithms, but less used in food science.

ABX testing differs from the other listed tests in that subjects are given two known different samples, and thus are able to compare them with an eye towards differences – there is an "inspection phase". While this may be hypothesized to make discrimination easier, no advantage has been observed in discrimination performance in ABX testing compared with other testing methods.[2]

Duo-trio in constant reference mode

Like triangle testing, but third is known to not be the odd one out. Intermediate between ABX (where which of the first is which – which is control, which is proposed new one – is stated), and triangle, where any of the three could be out.

Degree of difference (DoD)

This section is empty. You can help by adding to it. (March 2010)

Signal Detection Theory

This section is empty. You can help by adding to it. (July 2010)

Experimental design

This section is empty. You can help by adding to it. (July 2010)

Notes and references

  1. ^ ISO 4120:2004 Sensory analysis - Methodology - Triangle test
  2. ^ Huang, Y. T.; Lawless, H. T. (1998). "Sensitivity of the Abx Discrimination Test". Journal of Sensory Studies. 13 (2): 229–239. doi:10.1111/j.1745-459X.1998.tb00085.x.