Catch me if you can! How to beat GPT-4 with a 13B model

With similar rephrasing techniques, we observe consistent results in widely used coding and math benchmarks such as HumanEval and GSM-8K (shown in the cover figure). Therefore, being able to detect such rephrased samples becomes critical.

To address the risk of possible contamination, we propose a new contamination detection method “LLM decontaminator”.

This LLM decontaminator involves two steps:

1. For each test case, LLM decontaminator identifies the top-k training items with the highest similarity using the embedding similarity search.
2. From these items, LLM decontaminator generates k potential rephrased pairs. Each pair is evaluated for rephrasing using an advanced LLM, such as GPT-4.

Results show that our proposed LLM method works significantly better than existing methods on removing rephrased samples.

To compare different detection methods, we use MMLU benchmark to construct 200 prompt pairs using both the original and rephrased test sets. These comprised 100 random pairs and 100 rephrased pairs. The f1 score on these pairs provides insight into the detection methods’ ability to detect contamination, with higher values indicating more precise detection. As shown in the following table, except for the LLM decontaminator, all other detection methods introduce some false positives. Both rephrased and translated samples successfully evade the n-gram overlap detection. With multi-qa BERT, the embedding similarity search proves ineffective against translated samples. Our proposed LLM decontaminator is more robust in all cases with the highest f1 scores.

We apply the LLM decontaminator to widely used real-world datasets (e.g., the Stack, RedPajama, etc) and identify a substantial amount of rephrased samples. The table below displays the contamination percentage of different benchmarks in each training dataset.

Below we show some detected samples.

CodeAlpaca contains 20K instruction-following synthetic data generated by GPT, which is widely used for instruction fine-tuning (e.g., Tulu).

A rephrased example in CodeAlpaca is shown below.

This suggests contamination may subtly present in synthetic data generated by LLMs. In the Phi-1 report, they also discover such semantically similar test samples that are undetectable by n-gram overlap.

MATH is a widely recognized math training dataset that spans various mathematical domains, including algebra, geometry, and number theory. Surprisingly, we even find contamination between the train-test split in the MATH benchmark as shown below.

StarCoder-Data is used for training StarCoder and StarCoderBase, and it contains 783GB of code in 86 programming languages. In the StarCoder paper, the code training data was decontaminated by removing files that contained docstrings or solutions from HumanEval. However, there are still some samples detected by LLM decontaminator.

Based on the above study, we suggest the community adopt a stronger decontamination method when using any public benchmarks. Our proposed LLM decontaminator is open-sourced on GitHub. Here we show how to remove rephrased samples from training data using the LLM decontaminator tool. The following example can be found here.

Pre-process training data and test data. The LLM decontaminator accepts the dataset in jsonl format, with each line corresponding to a {"text": data} entry.

Run End2End detection. The following command builds a top-k similar database based on sentence bert and uses GPT-4 to check one by one if they are rephrased samples. You can select your embedding model and detection model by modifying the parameters.

In this blog, we show that contamination is still poorly understood. With our proposed decontamination method, we reveal significant previously unknown test overlap in real-world datasets. We encourage the community to rethink benchmark and contamination in LLM context, and adopt stronger decontamination tools when evaluating LLMs on public benchmarks. Moreover, we call for the community to actively develop fresh one-time exams to accurately evaluate LLMs. Learn more about our ongoing effort on live LLM eval at Chatbot Arena!

We would like to express our gratitude to Ying Sheng for the early discussion on rephrased samples. We also extend our thanks to Dacheng Li, Erran Li, Hao Liu, Jacob Steinhardt, Hao Zhang, and Siyuan Zhuang for providing insightful feedback.

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