Claiming Superiority and Equivalence Simultaneously
Ennis, D. M. (2017). IFPress, 20(2) 3-4.
The ASTM Standard Guide for Sensory Claim Substantiation specifies the criteria for superiority, equivalence, and unsurpassed claims. A summary of these types of claims is outlined in Figure 1.
Equivalence claims are based on a binary choice between two products and involve two bounds set at 45% and 55%. Within these bounds, two products are considered to be equivalent. Superiority claims are established when a choice probability (usually preference, but not always) exceeds 50%. Unsurpassed claims are made when the choice probability exceeds 45%. The idea behind this latter choice is based on the definition of an unsurpassed claim. An unsurpassed claim combines the concept of equivalence, with a 45% lower bound, and superiority, which has an upper bound of 100%.
Figure 2 illustrates these three types of claims and their corresponding bounds. The fact that these three types of claims involve different specifications can lead to a paradoxical outcome in claims support. All of these claims are based on statistical testing involving the appropriate null hypothesis, usually conducted at the 95% confidence level (Type I error of 5%).
In this technical report we will consider the problem created by these different specifications and explore the likelihood of a claims conflict.
Figure 1. Types of advertising claims.
Figure 2. Bounds defining advertising claim types.