A recent article in this journal examined bias in arbitration from the perspective of tribunal members. (Edgardo Muñoz and José Covarrubias Miranda, ‘Unconscious Bias in Arbitration: Case Law and the Path to Fairness’ (2025) 42 Journal of International Arbitration 4 435.) This article shifts the focus to bias in expert evidence and its impact on quantum assessments in international arbitration. Using an analogy involving estimates of the number of atoms in the universe, the authors illustrate how even small differences in assumptions can compound into significant distortions – including when tribunals ‘split the difference’ between opposing expert views. The paper argues that expert estimates can be best understood not as definitive truths but expressions of belief within a range of uncertainty, often underpinned by implicit Bayesian probability distributions. The authors highlight how directional bias in assumption selection – even within acceptable ranges – can lead to unreasonable outcomes. They propose remedies including joint expert reports, expert conferencing, transparent financial models, assumption-level disclosures and other tools. Tribunals are encouraged to interrogate not just the assumptions but the range and distribution of outcomes, and to consider discounting outlier estimates or misrepresentations by one expert. The article concludes that, while bias in expert evidence cannot be entirely eliminated, the use of appropriate tools to detect and address it can contribute to fair and well-reasoned quantum decisions.
Journal of International Arbitration