When two or more levels of an ingredient are presented for evaluation of an ideal level of that ingredient, the centering bias is introduced and the true optimum level is unlikely to be determined. Poulton (1979) and McBride (1982) have suggested methods for avoiding the centering bias, but their methods have never been tested. The purpose of this study was to check the validity of their methods. Three different ranges of sucrose concentrations were used to determine the optimum level of sucrose in lemonade. Twenty different judges were assigned to each of the three ranges and rated the samples on a just right scale. The unbiased just right sucrose concentrations, determined by the methods suggested by Poulton (1979) and McBride (1982), were 6.7% and 6.9%, respectively. A single stimulus presentation confirmed the results as being an unbiased optimum concentration.
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