This guide provides practical guidance on the responsible, appropriate, and inappropriate uses of quantitative metrics in research assessment, with a particular focus on evaluation of research project proposals, including the assessment of: the scientific quality of the proposal; the feasibility and credibility of the work plan; the prior experience, expertise, and relevant contributions of the applicants and team members, where these are part of the evaluation criteria. The guide does not aim to eliminate the use of quantitative information. Instead, it clarifies how metrics may be used responsibly, when they are misleading, and how they should be interpreted alongside expert judgement. Who is this guide for? External evaluators and reviewers Panel members, including rapporteurs and panel chairs Staff of research funding and performing organisations Applicants and their research teams, to improve transparency and mutual understanding The guide is relevant across disciplines and funding instruments, and is intended to support fairness, consistency, and quality of expert evaluation across the RDI ecosystem. This document was developed by UEFISCDI within the project ARIA – Advancing Responsible and Inclusive Assessment at UEFISCDI. The project is funded under the Horizon Europe programme through the CoARA Boost project Cascade Funding Call – Second Round. The ARIA project supports the advancement of responsible and inclusive research assessment practices, in alignment with the principles of the Agreement on Reforming Research Assessment. DisclaimerThis document reflects the views of the authors and contributors involved in its preparation and does not necessarily represent the official position or policies of the European Commission or other affiliated organisations.