d′ AND VARIANCE OF d′ FOR FOUR-ALTERNATIVE FORCED CHOICE (4-AFC)

The four-alternative forced choice (4-AFC) is one of a family of m-AFC tests used in Psychology. Based on a detection-theoretic model, for a given d′ it is slightly more powerful than the 3-AFC and 2-AFC. Although its potential use in sensory food science is limited, there are occasions when it will be used. Accordingly, tables of d′ values for given proportions of correct responses (pc) along with corresponding values of B, for computing variances, are given in this paper. Power comparisons are also made between 2-AFC, 3-AFC and 4-AFC tests. PRACTICAL APPLICATIONS For sensory difference testing, the choice of test will depend on several factors such as statistical power as well as various physiological and cognitive effects. Because of the wide variation in the sensory effects that food and personal product stimuli can have on judges, it is important to have a wide variety of test methods available. Therefore, even less common tests need to be considered. The 4-AFC can be used on occasions and it is certainly suitable for visual judgments. Accordingly, for this method, it is appropriate to have tables of d′ and B for computing variances.