Table 1.

A Pragmatic Approach to AOP Development and Evaluation

1. Development
1.1. Draw AOP blue-print diagram	Outline relevant AOP(s) and connect KEs by KERs to provide context and structure Identify and describe relevant KEs Identify canonical KERs versus KERs that require in-depth development
1.2. Develop individual KER	If canonical: rely on leading review articles from the open literature Use systematic review approaches for KER development when required
2. Evaluation and endorsement
2.1. Scientific review of KER	As a “KER Report” journal article similar to the existing “AOP Report” article format At the OECD EAGMST level
2.2.Endorsement of AOP	Assemble complete AOP or AOP network, completely or in part based on KERs that have already been reviewed OECD (WPHA/WNT) review and endorsement of entire AOP (network)

Abbreviations: AOP, adverse outcome pathway; KE, key event; KER, key event relationship; OECD, Organisation for Economic Co-operation and Development; EAGMST, Extended Advisory Group on Molecular Screening and Toxicogenomics; WPHA, Working Party on Hazard Assessment; WNT, Working Group of National Coordinators of the Test Guidelines program.