The Principles of Weight of Evidence Validation of Test Methods and Testing Strategies

This is the report of the 58th of a series of workshops organised by the European Centre for the Validation of Alternative Methods (ECVAM). The main objective of ECVAM, as defined in 1993 by its Scientific Advisory Committee (ESAC), is to promote the scientific and regulatory acceptance of alternative methods which are of importance to the biosciences, and which reduce, refine or replace the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures that would enable it to become well informed about the state of the art of non-animal test development and validation, and of opportunities for the possible incorporation of alternative methods into regulatory procedures. It was decided that this would be achieved through a programme of ECVAM workshops, each addressing a specific topic, and at which selected groups of independent international experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (1). The workshop was organised by Michael Balls and Valérie Zuang, and took place on 5–7 May 2004, at the Hotel Lido, Angera (VA), Italy, with participants from academia, industry, research, and national and international validation authorities. The aim was to discuss and define principles and criteria for validation via weight-of-evidence approaches, and to provide guidance on the performance of this type of validation. The outcome of the discussions and the recommendations agreed upon by the workshop participants are summarised in this report, which also takes into account some subsequent events and publications.