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Main Authors: Flamich, Gergely, Vilar, David, Peter, Jan-Thorsten, Freitag, Markus
Format: Preprint
Published: 2025
Subjects:
Online Access:https://arxiv.org/abs/2503.24013
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author Flamich, Gergely
Vilar, David
Peter, Jan-Thorsten
Freitag, Markus
author_facet Flamich, Gergely
Vilar, David
Peter, Jan-Thorsten
Freitag, Markus
contents The goal of translation, be it by human or by machine, is, given some text in a source language, to produce text in a target language that simultaneously 1) preserves the meaning of the source text and 2) achieves natural expression in the target language. However, researchers in the machine translation community usually assess translations using a single score intended to capture semantic accuracy and the naturalness of the output simultaneously. In this paper, we build on recent advances in information theory to mathematically prove and empirically demonstrate that such single-score summaries do not and cannot give the complete picture of a system's true performance. Concretely, we prove that a tradeoff exists between accuracy and naturalness and demonstrate it by evaluating the submissions to the WMT24 shared task. Our findings help explain well-known empirical phenomena, such as the observation that optimizing translation systems for a specific accuracy metric (like BLEU) initially improves the system's naturalness, while ``overfitting'' the system to the metric can significantly degrade its naturalness. Thus, we advocate for a change in how translations are evaluated: rather than comparing systems using a single number, they should be compared on an accuracy-naturalness plane.
format Preprint
id arxiv_https___arxiv_org_abs_2503_24013
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle You Cannot Feed Two Birds with One Score: the Accuracy-Naturalness Tradeoff in Translation
Flamich, Gergely
Vilar, David
Peter, Jan-Thorsten
Freitag, Markus
Computation and Language
The goal of translation, be it by human or by machine, is, given some text in a source language, to produce text in a target language that simultaneously 1) preserves the meaning of the source text and 2) achieves natural expression in the target language. However, researchers in the machine translation community usually assess translations using a single score intended to capture semantic accuracy and the naturalness of the output simultaneously. In this paper, we build on recent advances in information theory to mathematically prove and empirically demonstrate that such single-score summaries do not and cannot give the complete picture of a system's true performance. Concretely, we prove that a tradeoff exists between accuracy and naturalness and demonstrate it by evaluating the submissions to the WMT24 shared task. Our findings help explain well-known empirical phenomena, such as the observation that optimizing translation systems for a specific accuracy metric (like BLEU) initially improves the system's naturalness, while ``overfitting'' the system to the metric can significantly degrade its naturalness. Thus, we advocate for a change in how translations are evaluated: rather than comparing systems using a single number, they should be compared on an accuracy-naturalness plane.
title You Cannot Feed Two Birds with One Score: the Accuracy-Naturalness Tradeoff in Translation
topic Computation and Language
url https://arxiv.org/abs/2503.24013