Evaluation Methodology for Fate and Exposure Models

Abstract

The principles of model evaluation in terms of quality assurance, model validation, and software evaluation were elaborated and discussed with the intention to develop a suitable evaluation protocol for chemical risk assessment models. Since scientific theories and the mathematical models embedded therein cannot be proved as true, a pragmatic meaning of validation is required, of which the primary purpose is to increase the level of confidence that is placed in the model. The accuracy of the model outcome is a necessary, but insufficient criterion for the quality assurance of models. A wider approach is required which examines the scientific inference that can be made about models relative to their intended purpose. By reviewing the literature on the validation problem, it was found that all the facets of validation can be assigned to generic (internal) and task-specific (external) properties of a model. Appropriate and detailed quality criteria for fate and exposure assessment software have been recently developed. They are based on common standards for software supplemented by specific requirements for this field of application. Altogether, quality assurance of a model includes internal and external validation and addresses evaluation of the respective software. It should focus not only on the predictive capability of a model, but also on the strength of the theoretical underpinnings, the evidence supporting the model conceptualization, the database, and the software.