Proper Task Instructions and the Two-out-of-Five Test

Ennis, J. M., Rousseau, B., and Ennis, D. M.  (2012). IFPress, 15(4) 4-5.



Difference tests continue to play a prominent role as businesses investigate the sensory effects of ingredient or process changes. Even so, the importance of correct instructions in these tests is not always appreciated - incorrect instructions can reduce the ability of a test to detect real differences. The effect of instructions on the outcome of sensory difference testing was recognized when the difference between the 3-AFC and Triangle test was explained and when the relative power of difference testing methods was explored. This topic has resurfaced as other difference testing methods, such as the Two-out-of-Five test, have become more commonly used. In this report, we explain how incorrect instructions can sabotage a method, and we provide guidance for the optimal set of test instructions for the Two-out-of-Five test.


Figure 1. Three cases illustrating the difference between expected results under two instructions - “group the samples into a group of two and a group of three” (Grouping) and “choose the same pair” (Same Pair). The Same Pair instructions are marked by circling the selected responses and the Grouping instruction by underlining the groups.