Difference tests are the fundamental and most frequently used methods in sensory and consumer research. The most important questions difference tests must answer are: do various products differ from each other? And does the consumer detect the differences between various products?

Difference tests are used to measure small differences between products. For example, what is the effect of changing an ingredient, is the product like a reference sample, or does the packaging change the flavour or smell of a product?

The statistical principle behind every discrimination test should be to reject a null hypothesis (H0). For a difference test the null hypothesis states there is no detectable difference between two (or more) products. The alternative hypothesis H1 is that there is a detectable difference. If there is sufficient evidence to reject H0 in favour of the alternative hypothesis H1, then a difference can be recorded.

For a similarity test the null hypothesis states that there is a non-negligible difference. The alternative hypothesis is that there is no difference. If there is sufficient evidence to reject H0 in favour of the alternative hypothesis H1, then it can be concluded the products are similar.

However, failure to reject the null hypothesis should not be assumed evidence to accept it. The null hypothesis is formulated on the premise that all of the panellists 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 and the measured values are significantly different the null hypothesis can be rejected in favour of H1.

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