Discrimination testing

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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 trained panel to discriminate from one product to another.

Contents 1 Statistical basis 2 Types of test 2.1 Paired comparison 2.1.1 Advantages 2.1.2 Disadvantages 2.2 Duo-trio 2.2.1 Advantages 2.2.2 Disadvantages 2.3 Triangle 2.3.1 Advantages 2.3.2 Disadvantages 2.4 Degree of difference (DoD) 3 Signal Detection Theory 4 Experimental design

[edit] 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 favour of the alternative hypothesis, H_A:There is a detectable difference, then a difference can be recorded. However, failure to reject Ho 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 favour of H_A.

Tests used to decide whether or not to reject H₀ include binomial, χ² (Chi-squared), (others? Help needed)

[edit] 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.

[edit] 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 flavour, etc.

The probability for each assessor arriving at a correct response by guessing is p = 0.5

[edit] Advantages

One of the quickest and easiest of tests to execute. Can be used to determine whether formulation changes are detectable.

[edit] 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.

[edit] 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 p = 0.5

[edit] Advantages

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

[edit] Disadvantages

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

[edit] 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.

The probability for each assessor arriving at a correct response by guessing is p = 1 / 3

[edit] Advantages

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

[edit] Disadvantages

[edit] Degree of difference (DoD)

[edit] Signal Detection Theory

[edit] Experimental design

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