DUO tests

DUO tests are particularly suitable for this, i.e. tests in which pairs of samples are compared. These are tests such as the Paired Comparison Test (DIN Standard 10 954 [5], ISO Standard 5495 [6]) and the Comparison Test which does not involve a direct question about the difference. [Although it is called a Comparison Test in English, it actually deals with differences]... 

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). 

Everything else applies by analogy with the other tests. Statistical analysis is with the use of the relevant significance table as with DUO test. 

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

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... 

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.

The transmitting frequency / of the UVP-DUO systems is 4 MHz in all tests. The ultrasound wavelength X is 370 pm and the sound velocity in water c is 1,480 m/s. 100 mm ion exchange (Diaion) particles are added to the flow as flow tracers their ability to follow the liquid flow has been assessed using Basset s analysis (Melling, 1997). Owing to theoretical considerations, the size of the flow tracers must be larger than one quarter of the emitted ultrasonic burst (Met-Flow, 2002). 

At this point there s a little twist to our developing chicken-and-egg scenario. Even activated Stuart factor can t turn on prothrombin. Stuart factor and prothrombin can be mixed in a test tube for longer than it would take a large animal to bleed to death without any noticeable production of thrombin. It turns out that another protein, called accelerin, is needed to increase the activity of Stuart factor. The dynamic duo—accelerin and activated Stuart factor— cleave prothrombin fast enough to do the bleeding animal some good. So in this step we need two separate proteins to activate one proenzyme. 

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. 

Acid hydrolysates were added to a low aroma intensity white wine (ie the base wine), and the aroma properties of these samples were assessed by sensory descriptive analysis. In addition, the glycoside isolates from the Australian vineyards were subjected to glycoside hydrolase enzyme treatment, and duo-trio difference tests were performed on these hydrolysates added to a base wine. The volatile composition of each of the hydrolysates was investigated by GC/MS, and relationships between the two sets of data were determined. Finally, the glycoside concentration of each of the juices and skin extracts was determined by the glycosyl-glucose assay. 

In a separate part of this study, the aroma properties of glycoside enzyme hydrolysates added to a white base wine were assessed by duo-trio difference tests with 20 judges. The Australian samples only were evaluated. In tests comparing the... 

The test can be varied, e.g. several samples can be tested using several pairs (DUOs) against one control. 

Difference Testing at Different Stages of Cellar Storage. To determine whether any flavor change for the wines had occurred as a result of the juice treatments, duo-trio aroma difference tests were done between control replicates and treatment replicates after 6, 12, 20, and 27 months cellar storage. The first three series of comparisons were done between randomly selected pairs of control and treatment replicates. 

The technical performance of two systems (Duo , Hill-Rom Inc and Nimbus 3, Huntleigh Healthcare Ltd) was tested in 16 diabetics using PRI and tissue perfusion technique. The test was repeated using 14 healthy volunteras and lata- veraons (Duo 2 , Hill-Rom Inc and Nimbus Logic , Huntlei Healthcare Ltd) of each following the addition of specialised heel zones. 

Duo-trio In this test, the panelists receive three samples simultaneously one sample identified as a standard and two coded samples, one of which is the same formulation as the standard. A forced choice is required. Panelists have to recognize which of the... 

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). 

Duo-trio method is a three-product test in which one product is identified as R or Reference and the other two are coded. The subject s task is to indicate which coded sample is most like the reference. There are four orders of presentation - RjAB, RjBA, RjAB, and RjBA. 

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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