Triangle and tetrad protocols: Small sensory differences, resampling and consumer relevance

The objective of this research was twofold: first, the performance of the tetrad protocol was compared to that of the triangle test under conditions that could possibly lower its sensitivity, consequently resulting in the loss of its theoretical power advantage. Second, the same samples were compared with a preference test to investigate whether a no difference conclusion obtained with a discrimination test would consistently result in a non-significant preference (consumer relevance).The investigation involved sensory differences that could be deemed small (d′ values less than 1.0) as well as the comparison of resampling vs. no resampling conditions. 456 consumers performed tests using apple and orange juices for which slight sensory differences were created through dilution. In all conditions, the tetrad always exhibited a greater number of correct answers than the triangle, confirming its greater statistical power. Therefore, it was concluded that even for small sensory differences, and in conditions where sensory fatigue could play a greater role (resampling allowed), the tetrad test sill appears like a good alternative to the triangle. Also, the theoretical increase in performance predicted when allowing sample resampling was confirmed.For the preference study, the same stimuli were evaluated by 208 subjects. Consumer relevance was defined as a significant result between two products in a preference test (assuming no population segmentation). Such significant preferences were found for three out of the four conditions, including the one with the smallest difference for which a significant result had not been found with either the tetrad or triangle. The non-significant preference in the fourth condition was attributed to segmentation in the population.Therefore, this investigation confirmed further that the tetrad test is a viable alternative to the triangle test, as it exhibits a greater statistical power even in conditions that could potentially affect it negatively. Also, it was shown that a non-significant sensory difference can still result in a significant preference test, outlining the necessity to go beyond the simple use of a ‘more powerful’ discrimination test when making decisions and to define the actual consumer relevance of an underlying sensory difference.

• Tetrad test is more powerful than triangle test even for small sensory differences.
• Allowing stimulus resampling increases discrimination.
• Even with small sensory differences, consumers can exhibit a significant preference.
• Small but relevant sensory differences will be missed if insufficient sample size is used.