Tetrad testing is theoretically more powerful than Triangle testing, yet the addition of a fourth stimulus raises questions – it is possible that the addition of a fourth stimulus places such an additional demand on subjects that the theoretical advantage of the Tetrad test is lost. In this paper, we provide a guideline to compare results of Tetrad and Triangle. Specifically, it is roughly correct to say that as long as the effect sizes do not drop by more than one third for the same stimuli, then the Tetrad test remains more powerful than the Triangle test.We explain this guideline in terms of perceptual noise, illustrate its use in several examples and discuss the statistical considerations that accompany its use. To assist with statistical evaluation, we provide a table for finding the variance in the Tetrad-based measurement of the effect size. Finally, we show how the Thurstonian framework helps us to improve discrimination testing efficiency even when we do not seek additional power.
Ennis, J.M. (2012) Guiding the switch from triangle testing to tetrad testing. Journal of Sensory Studies. 27, 223–231.
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Guiding the switch from triangle testing to tetrad testing
Related webinar: Advances in Tetrad Testing
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