SelfCheckGPT

Project page for our paper "SelfCheckGPT: Zero-Resource Black-Box Hallucination Detection for Generative Large Language Models"
We investigated several variants of the selfcheck approach: BERTScore, QA, n-gram, and LLM-Prompting.
[18/07/2023] SelfCheck-NLI is added. Additional experiments show that using an entailment classifier (e.g. DeBERTa fine-tuned on Multi-NLI) performs well (see the results in the table below). SelfCheck-NLI method though requires considerably less computation than SelfCheck with LLM-prompting.

Code/Package

Installation

pip install selfcheckgpt

SelfCheckGPT Usage: BERTScore, QA, n-gram

There are three variants of SelfCheck scores in this package as described in the paper: SelfCheckBERTScore(), SelfCheckMQAG(), SelfCheckNgram(). All of the variants have predict() which will output the sentence-level scores w.r.t. sampled passages. You can use packages such as spacy to split passage into sentences. For reproducibility, you can set torch.manual_seed before calling this function. See more details in Jupyter Notebook demo/SelfCheck_demo1.ipynb

# Include necessary packages (torch, spacy, ...)
from selfcheckgpt.modeling_selfcheck import SelfCheckMQAG, SelfCheckBERTScore, SelfCheckNgram
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
selfcheck_mqag = SelfCheckMQAG(device=device) # set device to 'cuda' if GPU is available
selfcheck_bertscore = SelfCheckBERTScore(rescale_with_baseline=True)
selfcheck_ngram = SelfCheckNgram(n=1) # n=1 means Unigram, n=2 means Bigram, etc.

# LLM's text (e.g. GPT-3 response) to be evaluated at the sentence level  & Split it into sentences
passage = "Michael Alan Weiner (born March 31, 1942) is an American radio host. He is the host of The Savage Nation."
sentences = [sent.text.strip() for sent in nlp(passage).sents] # spacy sentence tokenization
print(sentences)
['Michael Alan Weiner (born March 31, 1942) is an American radio host.', 'He is the host of The Savage Nation.']

# Other samples generated by the same LLM to perform self-check for consistency
sample1 = "Michael Alan Weiner (born March 31, 1942) is an American radio host. He is the host of The Savage Country."
sample2 = "Michael Alan Weiner (born January 13, 1960) is a Canadian radio host. He works at The New York Times."
sample3 = "Michael Alan Weiner (born March 31, 1942) is an American radio host. He obtained his PhD from MIT."

# --------------------------------------------------------------------------------------------------------------- #
# SelfCheck-MQAG: Score for each sentence where value is in [0.0, 1.0] and high value means non-factual
# Additional params for each scoring_method:
# -> counting: AT (answerability threshold, i.e. questions with answerability_score < AT are rejected)
# -> bayes: AT, beta1, beta2
# -> bayes_with_alpha: beta1, beta2
sent_scores_mqag = selfcheck_mqag.predict(
    sentences = sentences,               # list of sentences
    passage = passage,                   # passage (before sentence-split)
    sampled_passages = [sample1, sample2, sample3], # list of sampled passages
    num_questions_per_sent = 5,          # number of questions to be drawn  
    scoring_method = 'bayes_with_alpha', # options = 'counting', 'bayes', 'bayes_with_alpha'
    beta1 = 0.8, beta2 = 0.8,            # additional params depending on scoring_method
)
print(sent_scores_mqag)
# [0.30990949 0.42376232]

# --------------------------------------------------------------------------------------------------------------- #
# SelfCheck-BERTScore: Score for each sentence where value is in [0.0, 1.0] and high value means non-factual
sent_scores_bertscore = selfcheck_bertscore.predict(
    sentences = sentences,                          # list of sentences
    sampled_passages = [sample1, sample2, sample3], # list of sampled passages
)
print(sent_scores_bertscore)
# [0.0695562  0.45590915]

# --------------------------------------------------------------------------------------------------------------- #
# SelfCheck-Ngram: Score at sentence- and document-level where value is in [0.0, +inf) and high value means non-factual
# as opposed to SelfCheck-MQAG and SelfCheck-BERTScore, SelfCheck-Ngram's score is not bounded
sent_scores_ngram = selfcheck_ngram.predict(
    sentences = sentences,   
    passage = passage,
    sampled_passages = [sample1, sample2, sample3],
)
print(sent_scores_ngram)
# {'sent_level': { # sentence-level score similar to MQAG and BERTScore variant
#     'avg_neg_logprob': [3.184312, 3.279774],
#     'max_neg_logprob': [3.476098, 4.574710]
#     },
#  'doc_level': {  # document-level score such that avg_neg_logprob is computed over all tokens
#     'avg_neg_logprob': 3.218678904916201,
#     'avg_max_neg_logprob': 4.025404834169327
#     }
# }

SelfCheckGPT Usage: NLI

Entailment (or Contradiction) score with input being the sentence and a sampled passage can be used as the selfcheck score. We use DeBERTa-v3-large fine-tuned to Multi-NLI, and we normalize the probability of "entailment" or "contradiction" classes, and take Prob(contradiction) as the score.

from selfcheckgpt.modeling_selfcheck import SelfCheckNLI
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
selfcheck_nli = SelfCheckNLI(device=device) # set device to 'cuda' if GPU is available

sent_scores_nli = selfcheck_nli.predict(
    sentences = sentences,                          # list of sentences
    sampled_passages = [sample1, sample2, sample3], # list of sampled passages
)
print(sent_scores_nli)
# [0.334014 0.975106 ] -- based on the example above

SelfCheckGPT Usage: (LLM) Prompt

In addition, we've tried using LLMs to assess information consistency in a zero-shot setup. We query a LLM to assess whether the i-th sentence is supported by the sample (as the context) using the following prompt.

Context: {}
Sentence: {}
Is the sentence supported by the context above?
Answer Yes or No:

Initial investigation showed that GPT-3 (text-davinci-003) will output either Yes or No 98% of the time, while any remaining outputs can be set to N/A. The output is converted to score: Yes -> 0.0, No -> 1.0, N/A -> 0.5. The inconsistency score is then calculated by averaging.

Dataset

The wiki_bio_gpt3_hallucination dataset currently consists of 238 annotated passages (v3). You can find more information in the paper or our data card on HuggingFace: https://huggingface.co/datasets/potsawee/wiki_bio_gpt3_hallucination. To use this dataset, you can either load it through HuggingFace dataset API, or download it directly from below in the JSON format.

Update

We've annotated GPT-3 wikibio passages further, and now the dataset consists of 238 annotated passages. Here is the link for the IDs of the first 65 passages in the v1.

Option1: HuggingFace

from datasets import load_dataset
dataset = load_dataset("potsawee/wiki_bio_gpt3_hallucination")

Option2: Manual Download

Download from our Google Drive, then you can load it in python:

import json
with open("dataset.json", "r") as f:
    content = f.read()
dataset = json.loads(content)

Each instance consists of:

gpt3_text: GPT-3 generated passage
wiki_bio_text: Actual Wikipedia passage (first paragraph)
gpt3_sentences: gpt3_text split into sentences using spacy
annotation: human annotation at the sentence level
wiki_bio_test_idx: ID of the concept/individual from the original wikibio dataset (testset)
gpt3_text_samples: list of sampled passages (do_sample = True & temperature = 1.0)

Experiments

Probability-based baselines (e.g. GPT-3's probabilities)

As described in our paper, probabities (and generation entropies) of the generative LLM can be used to measure its confidence. Check our example/implementation of this approach in demo/experiments/probability-based-baselines.ipynb

Experimental Results

Full details can be found in our paper.
Note that our new results show that LLMs such as GPT-3 (text-davinci-003) or ChatGPT (gpt-3.5-turbo) are good at text inconsistency assessment. Based on this finding, we try SelfCheckGPT-Prompt where each sentence (to be evaluated) is compared against each and every sampled_passage by prompting ChatGPT. SelfCheckGPT-Prompt is the best-performing method.

Results on the wiki_bio_gpt3_hallucination dataset.

Method	NonFact (sent-lvl)	Factual (sent-lvl)	PCC (passage-lvl)
GPT-3 Avg(-logP)	83.21	53.97	57.04
SelfCheck-BERTScore	81.96	44.23	58.18
SelfCheck-QA	84.26	48.14	61.07
SelfCheck-Unigram	85.63	58.47	64.71
SelfCheck-NLI	92.50	66.08	74.14
SelfCheck-Prompt	93.42	67.09	78.32

Miscellaneous

MQAG (Multiple-choice Question Answering and Generation) was proposed in our previous work. Our MQAG implementation is included in this package, which can be used to: (1) generate multiple-choice questions, (2) answer multiple-choice questions, (3) obtain MQAG score.

MQAG Usage

from selfcheckgpt.modeling_mqag import MQAG
mqag_model = MQAG()

It has three main functions: generate(), answer(), score(). We show an example usage in demo/MQAG_demo1.ipynb

Acknowledgements

This work is supported by Cambridge University Press & Assessment (CUP&A), a department of The Chancellor, Masters, and Scholars of the University of Cambridge, and the Cambridge Commonwealth, European & International Trust.

Citation

@misc{manakul2023selfcheckgpt,
      title={SelfCheckGPT: Zero-Resource Black-Box Hallucination Detection for Generative Large Language Models},
      author={Potsawee Manakul and Adian Liusie and Mark J. F. Gales},
      year={2023},
      eprint={2303.08896},
      archivePrefix={arXiv},
      primaryClass={cs.CL}
}

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