Performance indices and isotropic scaling factors in sensory profiling

A new procedure for the determination of the isotropic scaling factors in Generalised Procrustes Analysis is discussed. A noteworthy feature of this procedure is that each isotropic scaling factor is shown to be the product of a standardisation scalar which adjusts for the differences in range of scoring among assessors, and a performance index. An overall performance index for the whole panel is also discussed. The performance indices can be useful in improving the performance of the panel by pointing out whether further training is required for the whole panel or for some specific assessors. Once the isotropic scaling factors are determined, it is possible to derive a group average configuration using one of several algorithms proposed in the statistical literature which aim at matching a set of configurations by means of rotations. A data set is analysed and a simulation study is undertaken in order to demonstrate the method, and the outcomes are compared to those obtained by means of Gower's algorithm for Generalised Procrustes Analysis.