Abstract
Tetrad test is theoretically more powerful than triangle test. However, in the presence of sensory fatigue-caused foods, the advantage of the tetrad test is lost. In case of alcohol beverage containing 50%abv, triangle test is recommended as a standard protocol because the sensory fatigue caused by ethanol is great enough that leads tetrad test be less powerful than triangle test.
 In this study, the association between alcohol concentration and power of tetrad as well as triangle was established in cases of alcoholic beverages lower than 50%abv. Based on this result, the alcohol concentration at which the tetrad test is more powerful than triangle test was determined.
 The power comparisons between triangle test and tetrad test were extended to some alcohol beverages containing 40 and 30%abv. 240 panelists were divided into 8 panels. In each session, both triangle test and tetrad test were performed by a same panel (N = 30) on the samples made from the same alcohol beverage basic with and without citric acid. There were four sessions for each product that corresponded with four increasingly levels of added citric acid (2.192, 3.1, 4.384, 6.2g/L). By applying logistic regression, the power comparison between two tests was based on the correct response proportions (Pc) which were predicted from two variables: acid concentration and protocol.
 Multivariate logistic regression analysis indicated that there was 84% chance and 38% chance for the tetrad’s Pc to be higher than triangle’s Pc in case of beverage containing 30 and 40%abv, respectively. The results shown that increase alcohol concentration will reduce the power of both triangle and tetrad tests. It was noteworthy that tetrad test was affected more strongly by alcohol than triangle test.
 These findings suggest that the triangle test can be used as a suitable testing methodology for alcoholic beverages which alcohol concentration is not lower than 40%abv. In case of beverage containing 30%abv, triangle test should be replaced by tetrad test due to the increased reliability of information.
Highlights
Power analysis can evaluate the efficiency of a discrimination test
In case of beverage containing 30%abv, we have more than 50% chances that the tetrad test returned greater numbers of correct responses than the triangle test
Power of the tetrad and triangle tests were compared at different alcohol concentrations
Summary
Power analysis can evaluate the efficiency of a discrimination test. The more powerful a discrimination test, the less likely it is to lead to a type II error. It is critical to choose a discrimination test which minimizes type II error (i.e., that is higher in power). The power of a discrimination test is considered as the most important issue to be considered when choosing methods [1]. There is a large body of work evaluating discrimination testing methods by comparing their power. In a more comprehensive study, Bi [4], Bi and Ennis [1] ranked discrimination tests in order of increasing statistical power as follow: duo-trio, triangle, A-not A, 2-AFC, 3-AFC. This suggests that specified tests are preferable to unspecified tests when statistical power is concerned but are less applied in food evaluation practice because food is considered a complex and multi-dimensional system [6]
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