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.
This article appears as:
Ennis, J.M. (2012) Guiding the switch from triangle testing to tetrad testing. Journal of Sensory Studies. 27, 223–231.
Colleagues can request this journal article here:
Guiding the switch from triangle testing to tetrad testing
Related webinar: Advances in Tetrad Testing
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