DUO-TRIO tests

In the duo-trio test one presents to each panellist (or subject ) an identified reference sample, followed by two coded samples, one of which matches the reference sample (Fig. 38.2). The subjects are asked to indicate which of the two coded samples matches the reference. If enough correct replies are obtained the two coded samples are perceived as different. Table 38.2 gives the critical values 

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Fig. 38.2. Duo-trio test two different products are presented the assessor has to indicate which of these two is similar to a third product.

Difference testing has not changed greatly over the years. The triangle test and duo-trio test remain popular and well-accepted, although much effort has been extended to prove one better than the other. The best advice is to use the one that fits your test situation. 

As the name suggests, this DUO-TRIO test (ISO Standard 10399 [8]) lies between the two types of test mentioned above. As a rule, it is a DUO test in which 2 samples are tested against a THIRD sample (standard, control, etc.) thus making it a TRIO. The difference to the triangle test, however, is that in principle only 2 samples are being processed . As with the Duo test, the statistical probability that it will be done CORRECTLY is assumed to be 50% (p= 1/2), whereas with the triangle test it is only 33 1/3% (p = 1/3). 

Table 6.1 Significance Table for DUO Test and DUO-TRIO Test [9]...

Difference testing can be useful tools for assessing panelist s skills. Methods such as the triangle and duo-trio tests are what are communally known as forced choice discrimination tests because panelists are presented with multiple samples and must decide which examples are the same and which are different. These tests can also be used in assessing the impact of changes in supply chain and production techniques. Succinct descriptions of these and other discrimination tests can be found in Bamforth (2014) and Simpson (2006). More in-depth discussions of these techniques are covered by Kilcast (2010), Meilgaard et al. (2007) and Stone et al. (2012). 

Previous research on the perception threshold has shown that the elderly were able to perform 2-AFC or 3-AFC type tasks (Mojet et al., 2001) for a review see Methven et al. (2012). As a consequence, it may be relevant to conduct discriminative tasks with elderly people so as to, for example, check if any improvement brought to the product has actually been perceived by this population or not. Yet, as attentional capacities decline with age, we recommend choosing duo-trio tests, or paired comparison tests, rather than a triangle test or tetrad. Indeed, the latter require comparing simultaneously more samples than the former, and are therefore more costly from a cognitive point of view. 

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