Transitioning from Proportion of Discriminators to Thurstonian d
Rousseau, B., Ennis, D. M., and Ennis, J. M. (2013). IFPress, 16(2) 3-4.
In a previous technical report we discussed a commonly used measure of sensory difference, the proportion of discriminators (Pd), and explained that this measure is method specific. We concluded that:
“The concept of the proportion of discriminators is intuitive and appealing. Unfortunately, it is also method-specific and one can achieve very different values using different methods, which reduces its appeal as a management criterion. The use of a method–independent index, such as the Thurstonian d′, can provide more stable and accurate information that may be valuable in a decision that involves the consideration of consumers’ ability to discriminate between alternate product formulations.”
Many companies have implemented sensory discrimination programs using Pd as a parameter for power calculations. Since this measure has shortcomings, there is a need to consider a unit that is method-independent such as the Thurstonian d. Fortunately, tools exist that permit the translation of a method-specific Pd into the corresponding d value. In this report we discuss how these tools can be used in practice.
Figure 4. Relationship of d to proportion correct and proportion discriminators for the triangle and tetrad tests; example of a Pd of 25%.