Two studies were conducted to determine the effect of panelist participation frequency and specific aspects of questionnaire design on overall acceptance scoring in consumer central location tests. Regarding participation frequency, research subjects who participate frequently in some survey types are known to provide responses that differ from subjects who participate less frequently, known as panel conditioning. With respect to questionnaire design, overall acceptance (OA) question placement and usage of pre-evaluation instructions (PEI) in questionnaires for food sensory analysis may bias consumers' scores via carry-over effects. To investigate these concerns, data from consumer sensory panels previously conducted at a central location, spanning 11 years and covering a broad range of food product categories, was extracted, compiled, and analyzed. For the first study, data was analyzed to determine evidence of panel conditioning by measuring the effect of participation frequency on mean consumer OA scoring among frequent, moderate, and infrequent participants. Practical significance and occurrence of panel conditioning, defined as mean scoring differences of ≥ 0.50 on a discrete 9-point scale hedonic point, were examined. Results indicate that for overall acceptance, in general, mean scoring differences were not practically significant and did not signify occurrence of panel conditioning. For the second study, OA question placement was studied with categories designated as first (the first evaluation question following demographic questions), after non-gustation questions (immediately following questions that do not require panelists to taste the product), and later (following all other hedonic and just-about-right questions, but occasionally before ranking, open-ended comments, and/or intent to purchase questions). Additionally, each panel was categorized as having or not having PEI in the questionnaire; PEI are instructions that appear immediately before the first evaluation question and show panelists all attributes they will evaluate prior to receiving test samples. Post-panel surveys were administered regarding the self-reported effect of PEI on panelists' evaluation experience. OA scores were analyzed and compared (1) between OA question placement categories and (2) between panels with and without PEI. For most product categories, OA scores tended to be lower when asked later in the questionnaire, suggesting evidence of a carry-over effect. Usage of PEI increased OA scores by 0.10 of a 9-point hedonic scale point, which is not practically significant. Post-panel survey data showed that presence of PEI typically improved the panelists' experience. Using PEI does not appear to introduce a meaningful carry-over effect.

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