Development of an improved two-alternative choice (2AC) sensory test protocol based on the application of the asymmetric dominance effect

The goal of this study was to demonstrate that participants in a 2AC test can be induced to select the no-difference alternative by modifying the design of test ballots. Four different protocols (2AFC, 2AC, and two modified versions of 2AC) were evaluated; the two modified versions consisted of one where the judges were told that samples were the same and another where an “I do not know” alternative was included. Aqueous sucrose solutions were employed to evaluate the discriminative efficiency of the tests. Both 2AC modified versions effectively increased (p ⩽ 0.05) the proportion of judges choosing the “no-difference” option. The discriminative efficiency of the “I do not know” 2AC version was about three times higher than that of the other three protocols. This study demonstrated that it is possible to modify the proportion of judges choosing the no-difference option through ballot design, and that free-choice protocols may show much higher discriminative power than forced-choice tests when the no-difference alternative is properly used.