Pairing Detection of Off-Flavor in Orange Juice with Preference Tests

Paired preference tests and placebo placement: 1. Should placebo pairs be placed before or after the target pair?

One type of paired preference test uses the 'target' pair of stimuli under consideration to record the measured preferences (prefer A, Prefer B, 'no preference') and a second putatively identical control pair, the 'placebo' pair (AA or BB) to indicate 'false' preferences, unrelated to the target pair, elicited by the effects of the testing situation. From the literature there is disagreement regarding whether it is important to place a placebo pair before or after its corresponding target pair, to elicit a greater proportion of 'no preference' responses. This is important, because the higher the frequency of 'no preference' responses in the placebo pair, the more powerful will be the chi-squared style analysis, which determines whether the target pair displays a significant preference or not. It has been hypothesized that placing the placebo pair after the target pair would elicit more 'no preference' responses in the placebo, because the consumers would have had a chance to experience the difference in sensory characteristics of the two stimuli in the target pair. Using a related samples design, the hypothesis was confirmed although the difference between placebos placed before and after the target was not always significant. It was hypothesized that this lack of significance was caused by greater variance among the items being assessed, making it more difficult to decide whether a putatively placebo pair, in the context of the experiment, was really 'identical'. Psychological adjustments in the consumers were discussed in terms of difference and preference tau criteria. A boost in the proportion of 'no preferences' was observed for the placebo pair built into the triadic preference test, this was explained by the experimenter gaining some control over the consumers' preference tau criteria.

Paired preference tests and placebo placement: 2. Unraveling the effects of stimulus variance

From the literature on paired preference testing, there has been disagreement regarding whether a placebo pair would have a significantly higher frequency of 'no preference' responses if it were to be placed for assessment after its corresponding target pair rather than before. This can be important, because the higher the frequency of 'no preference' responses in the placebo pair, the more powerful will be any chi-squared related analysis, which determines whether the target pair indicates a significant preference or not. In the first paper in this series, it was shown, that indeed a placebo placed after the target pair induced a higher proportion of consumers to respond with a 'no preference'. However, the response was uneven. For some stimuli, the response was strong and significant, for others it was weaker and not significant. It was hypothesized that the weak response could be due to greater variance among the individual stimuli in the placebo sample to be tasted. The effect was confirmed using a priori chosen high and low variance stimuli. Further evidence was obtained from predictions for preference tau criterion levels and frequency of preference changes between two target pairs. All these indicated that the weaker response of some stimuli was due to a higher level of variance among the individual stimuli.