BASE SIZE IN PRODUCT TESTING - A PSYCHOPHYSICAL VIEWPOINT AND ANALYSIS

In the applied world of product testing the appropriate number of pane lists (base size) involves technical and business considerations. Base sizes range from very low (around six; used in expert panelist profil ing) to high (hundreds; used in product tests by marketing researchers ). Often base sizes are dictated by the requirement that the project i dentify statistical differences between or among samples. The probabil istic analysis of differences (significance vs. insignificance) derive s from statistical theory, with bare size used as a method to influenc e the sampling error (variability). This paper looks at bare sizes ano ther way-from the viewpoint of psychophysical scaling. The issue then can be re-stated as 'what is the necessary base size at which the aver age rating stabilizes?' Empirical data suggest that base sizes of 40-5 0 panelists generate stable averages, and that beyond the 80 panelists the average is not particularly affected by the base size. These resu lts hold for actual data for a variety of products, and for different types of attributes, specifically sensory (amount of a characteristic) , and hedonic (liking of a characteristic). (C) 1997 Elsevier Science Ltd.