Validating and comparing predictive models

The bias and accuracy factors introduced by Ross [Ross, T., 1996. Indices f or performance evaluation of predictive models in food microbiology. J. App l Bacteriol. 81, 501-508] for the evaluation of the performance of models i n 'predictive food microbiology' are refined by basing the calculation of t hose measures on the mean square differences between predictions and observ ations. The use of the indices is extended by presenting formulae and metho ds which enable evaluation of the difference between alternative models for growth of an organism of interest over a domain of environmental factors. This is done by calculating the integral mean of the square differences bet ween the models under investigation over the domain of the environmental va riables common to those models, or a sub-region of it. The use of the techn iques is exemplified by evaluating the difference between four published mo dels for the growth rate of psychrotrophic pseudomonads. (C) 1999 Elsevier Science B.V. All rights reserved.