A Systematic Study and Comprehensive Evaluation of ChatGPT on Benchmark Datasets
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Abstract (arXiv)
The development of large language models (LLMs) such as ChatGPT has brought a lot of attention recently. However, their evaluation in the benchmark academic datasets remains under-explored due to the difficulty of evaluating the generative outputs produced by this model against the ground truth. In this paper, we aim to present a thorough evaluation of ChatGPT's performance on diverse academic datasets, covering tasks like question-answering, text summarization, code generation, commonsense reasoning, mathematical problem-solving, machine translation, bias detection, and ethical considerations. Specifically, we evaluate ChatGPT across 140 tasks and analyze 255K responses it generates in these datasets. This makes our work the largest evaluation of ChatGPT in NLP benchmarks. In short, our study aims to validate the strengths and weaknesses of ChatGPT in various tasks and provide insights for future research using LLMs. We also report a new emergent ability to follow multi-query instructions that we mostly found in ChatGPT and other instruction-tuned models. Our extensive evaluation shows that even though ChatGPT is capable of performing a wide variety of tasks, and may obtain impressive performance in several benchmark datasets, it is still far from achieving the ability to reliably solve many challenging tasks. By providing a thorough assessment of ChatGPT's performance across diverse NLP tasks, this paper sets the stage for a targeted deployment of ChatGPT-like LLMs in real-world applications.
Key facts. Cited by 123 papers in the map (data through 7 Oct 2026). Builds on 147 of its 232 references that are in the map. First posted on arXiv 29 May 2023.
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147 of 232 references.
References · 147
- 2017Attention Is All You Needcited by 59,932
- 2018BERT: Pre-training of Deep Bidirectional Transformers for Language Understandingcited by 40,204
- 2020Language Models are Few-Shot Learnerscited by 32,199
- 2022Training language models to follow instructions with human feedbackcited by 15,712
- 2019Exploring the Limits of Transfer Learning with a Unified Text-to-Text Transformercited by 14,491
- 2021LoRA: Low-Rank Adaptation of Large Language Modelscited by 14,084
- 2023LLaMA: Open and Efficient Foundation Language Modelscited by 13,958
- 2019RoBERTa: A Robustly Optimized BERT Pretraining Approachcited by 13,266
- 2021Training Verifiers to Solve Math Word Problemscited by 9,743
- 2021Evaluating Large Language Models Trained on Codecited by 8,053
- 2020Measuring Massive Multitask Language Understandingcited by 7,768
- 2019BART: Denoising Sequence-to-Sequence Pre-training for Natural Language Generation, Translation, and Comprehensioncited by 5,874
38 more
- 2022PaLM: Scaling Language Modeling with Pathwayscited by 5,304
- 2021Measuring Mathematical Problem Solving With the MATH Datasetcited by 5,203
- 2018GLUE: A Multi-Task Benchmark and Analysis Platform for Natural Language Understandingcited by 4,854
- 2018Think you have Solved Question Answering? Try ARC, the AI2 Reasoning Challengecited by 4,710
- 2019DistilBERT, a distilled version of BERT: smaller, faster, cheaper and lightercited by 4,243
- 2019HellaSwag: Can a Machine Really Finish Your Sentence?cited by 4,018
- 2021Prefix-Tuning: Optimizing Continuous Prompts for Generationcited by 3,878
- 2021The Power of Scale for Parameter-Efficient Prompt Tuningcited by 3,769
- 2021Finetuned Language Models Are Zero-Shot Learnerscited by 3,747
- 2021Program Synthesis with Large Language Modelscited by 3,509
- 2021Switch Transformers: Scaling to Trillion Parameter Models with Simple and Efficient Sparsitycited by 3,014
- 2022Scaling Instruction-Finetuned Language Modelscited by 2,997
- 2022Training Compute-Optimal Large Language Modelscited by 2,927
- 2021TruthfulQA: Measuring How Models Mimic Human Falsehoodscited by 2,919
- 2017TriviaQA: A Large Scale Distantly Supervised Challenge Dataset for Reading Comprehensioncited by 2,895
- 2019PIQA: Reasoning about Physical Commonsense in Natural Languagecited by 2,818
- 2019ALBERT: A Lite BERT for Self-supervised Learning of Language Representationscited by 2,772
- 2020The Pile: An 800GB Dataset of Diverse Text for Language Modelingcited by 2,346
- 2019BoolQ: Exploring the Surprising Difficulty of Natural Yes/No Questionscited by 2,140
- 2018Can a Suit of Armor Conduct Electricity? A New Dataset for Open Book Question Answeringcited by 2,114
- 2022Beyond the Imitation Game: Quantifying and extrapolating the capabilities of language modelscited by 1,970
- 2022BLOOM: A 176B-Parameter Open-Access Multilingual Language Modelcited by 1,968
- 2019BioBERT: a pre-trained biomedical language representation model for biomedical text miningcited by 1,935
- 2022Challenging BIG-Bench Tasks and Whether Chain-of-Thought Can Solve Themcited by 1,767
- 2019SuperGLUE: A Stickier Benchmark for General-Purpose Language Understanding Systemscited by 1,718
- 2018Know What You Don't Know: Unanswerable Questions for SQuADcited by 1,538
- 2021Multitask Prompted Training Enables Zero-Shot Task Generalizationcited by 1,462
- 2019SciBERT: A Pretrained Language Model for Scientific Textcited by 1,404
- 2022Solving Quantitative Reasoning Problems with Language Modelscited by 1,359
- 2023Is Your Code Generated by ChatGPT Really Correct? Rigorous Evaluation of Large Language Models for Code Generationcited by 1,332
- 2018Don't Give Me the Details, Just the Summary! Topic-Aware Convolutional Neural Networks for Extreme Summarizationcited by 1,308
- 2017Get To The Point: Summarization with Pointer-Generator Networkscited by 1,281
- 2022LaMDA: Language Models for Dialog Applicationscited by 1,218
- 2021Scaling Language Models: Methods, Analysis & Insights from Training Gophercited by 1,199
- 2023PaLM 2 Technical Reportcited by 1,154
- 2015Teaching Machines to Read and Comprehendcited by 1,039
- 2020Domain-Specific Language Model Pretraining for Biomedical Natural Language Processingcited by 996
- 2019Publicly Available Clinical BERT Embeddingscited by 995
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