Developing the triadic preference test: A mystery solved and a bias avoided

Abstract

The development of the triadic preference test and how it differed cognitively from other paired preference tests involving placebo pairs, is outlined. The test elicited a far greater proportion of ‘no preference’ responses from placebo pairs than expected, thus increasing its power. Although the reasons for this were not fully understood at the time the test was first introduced, a necessary understanding of the mechanism later evolved with the help of a recently published systems analysis and some results from social psychology. Later, to this was added a warning that the test was prone to odd sample bias. The bias could be avoided by adjustment of the counterbalancing controls, using a method similar to that for the replicated duo-trio difference-preference test. Unfortunately, there had been some misunderstanding about the instructions in the warning, so an experiment was performed to re-affirm the warning using the correct instructions. The experiment confirmed that the test was prone to the odd sample bias, so that the counterbalancing changes were adopted. Yet, the bias was not present for all products being tested. This suggested that there are still some questions to be answered for what is still an under-researched area.