Validation of the models

Although many international regulatory bodies recognize the potential benefits of quantitative structure-activity relationship (QSAR) techniques, they are scarcely used in real applications. Some general principles are listed, but the lack of guidelines and standardized protocols accepted and used by all research groups prevents an effective world-wide development of such strategies. The use of appropriate statistical validation tools, such as the training and test set or others, should be adopted for predictive models not only in the case of QSAR based on descriptors but also in the case of models based on rules. In other words, the rules that are defined as appropriate for predictive purposes should also be validated. The statistical tools should prove the capability of the model to be valid in a general way-to be predictive for compounds not used in development of the model.