As easy as PIE: understanding when pruning causes language models to disagree

Fuente: arXiv
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Main Authors: Tropeano, Pietro, Maistro, Maria, Ruotsalo, Tuukka, Lioma, Christina
Format: Preprint
Published: 2025
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author Tropeano, Pietro
Maistro, Maria
Ruotsalo, Tuukka
Lioma, Christina
author_facet Tropeano, Pietro
Maistro, Maria
Ruotsalo, Tuukka
Lioma, Christina
contents Language Model (LM) pruning compresses the model by removing weights, nodes, or other parts of its architecture. Typically, pruning focuses on the resulting efficiency gains at the cost of effectiveness. However, when looking at how individual data points are affected by pruning, it turns out that a particular subset of data points always bears most of the brunt (in terms of reduced accuracy) when pruning, but this effect goes unnoticed when reporting the mean accuracy of all data points. These data points are called PIEs and have been studied in image processing, but not in NLP. In a study of various NLP datasets, pruning methods, and levels of compression, we find that PIEs impact inference quality considerably, regardless of class frequency, and that BERT is more prone to this than BiLSTM. We also find that PIEs contain a high amount of data points that have the largest influence on how well the model generalises to unseen data. This means that when pruning, with seemingly moderate loss to accuracy across all data points, we in fact hurt tremendously those data points that matter the most. We trace what makes PIEs both hard and impactful to inference to their overall longer and more semantically complex text. These findings are novel and contribute to understanding how LMs are affected by pruning. The code is available at: https://github.com/pietrotrope/AsEasyAsPIE
format Preprint
id arxiv_https___arxiv_org_abs_2503_21714
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle As easy as PIE: understanding when pruning causes language models to disagree
Tropeano, Pietro
Maistro, Maria
Ruotsalo, Tuukka
Lioma, Christina
Computation and Language
Language Model (LM) pruning compresses the model by removing weights, nodes, or other parts of its architecture. Typically, pruning focuses on the resulting efficiency gains at the cost of effectiveness. However, when looking at how individual data points are affected by pruning, it turns out that a particular subset of data points always bears most of the brunt (in terms of reduced accuracy) when pruning, but this effect goes unnoticed when reporting the mean accuracy of all data points. These data points are called PIEs and have been studied in image processing, but not in NLP. In a study of various NLP datasets, pruning methods, and levels of compression, we find that PIEs impact inference quality considerably, regardless of class frequency, and that BERT is more prone to this than BiLSTM. We also find that PIEs contain a high amount of data points that have the largest influence on how well the model generalises to unseen data. This means that when pruning, with seemingly moderate loss to accuracy across all data points, we in fact hurt tremendously those data points that matter the most. We trace what makes PIEs both hard and impactful to inference to their overall longer and more semantically complex text. These findings are novel and contribute to understanding how LMs are affected by pruning. The code is available at: https://github.com/pietrotrope/AsEasyAsPIE
title As easy as PIE: understanding when pruning causes language models to disagree
topic Computation and Language
url https://arxiv.org/abs/2503.21714