Jagoda Mazur, Greta Hofstra, Anne Goldman, Donya Germain
A contrast effect occurs when presentation of a sample of high flavour intensity or good quality just before one of a weak flavour intensity (or poor quality) causes the second sample to receive a lower rating than if it has been rated alone (1, 2, 3). Designs, which are balanced for carryover effects, have been recommended to minimize these effects (4).
Contrast effects in food acceptability assessment were examined for consumers evaluating soy beverages. Users of both vanilla flavoured and unflavoured (plain) soy beverages assessed paired, two vanilla and two unflavoured soy beverages for overall acceptability and specific attribute acceptability. The evaluation was carried out either in a single session (one day) or in two sessions (over two days). Presentation of the products was fully balanced over the two flavours and within each of the two flavours to prevent occurrence of carryover effects.
Based on the results, the position of the vanilla flavoured beverage, before or after the unflavoured beverage, impacted the overall acceptability of the unflavoured (plain) soy beverage. The unflavoured beverage was deemed to be significantly less likeable when it was presented after the more palatable vanilla beverage than when the unflavoured beverage was presented first.
This study demonstrates that even fully balanced designs do not entirely prevent a contrast effect from occurring and causing a significance bias in judgments of food acceptability. This effect was evident for both sessions (same day or next day).
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3. Schifferstein, H. N. J., & Kuiper, W. E. (1997). Sequence effects in hedonic judgments of taste stimuli. Perception and Psychophysics, 56, 900–912.
4. Wakeling, I. N., & MacFie, H. J. H. (1995). Designing consumer trials balanced for first and higher orders of carry-over effect when only a subset of k samples from t may be tested. Food Quality and Preference, 6, 299–308