It is widely believed that preference data are more sensitive than rated acceptability, since two products can get the same acceptability rating on a category scale, but there might be a slight preference for one over the other. Empirical data supporting this belief are not found in the scientific literature. Furthermore, preference tests tell little or nothing about the overall level of acceptance, since one product might be preferred over the other, but both might be unacceptable. On the other hand, acceptability ratings can provide information on the direction of presumed preference. The emphasis in both procedures is on obtaining a representative sample of consumers for the test.
Several principles apply.
First, laboratory personnel generally make poor choices for participants. They come with a technical and potentially biased frame of reference for evaluating the products. If consumers are recruited, they should be regular users or purchasers of the product. With such larger samples, it is possible to look for segments or groups of consumers with different preference patterns, rather than simply looking at overall means for different products or other measures of central tendency.