Multi-group Uncertainty Quantification for Long-form Text Generation (2407.21057v1)

Abstract: While LLMs are rapidly moving towards consumer-facing applications, they are often still prone to factual errors and hallucinations. In order to reduce the potential harms that may come from these errors, it is important for users to know to what extent they can trust an LLM when it makes a factual claim. To this end, we study the problem of uncertainty quantification of factual correctness in long-form natural language generation. Given some output from a LLM, we study both uncertainty at the level of individual claims contained within the output (via calibration) and uncertainty across the entire output itself (via conformal prediction). Moreover, we invoke multicalibration and multivalid conformal prediction to ensure that such uncertainty guarantees are valid both marginally and across distinct groups of prompts. Using the task of biography generation, we demonstrate empirically that having access to and making use of additional group attributes for each prompt improves both overall and group-wise performance. As the problems of calibration, conformal prediction, and their multi-group counterparts have not been extensively explored previously in the context of long-form text generation, we consider these empirical results to form a benchmark for this setting.

Multi-group Uncertainty Quantification for Long-form Text Generation

The paper "Multi-group Uncertainty Quantification for Long-form Text Generation" by Terrance Liu and Zhiwei Steven Wu addresses a significant problem in the deployment of LLMs for consumer-facing applications: the need to quantify and communicate the uncertainty of factual correctness in generated long-form text. The emphasis on managing factual errors and hallucinations in LLM outputs is critical, especially as these models are increasingly used in real-world applications.

Core Contributions

The paper introduces methods to quantify uncertainty in LLM outputs at two levels:

1. Individual Claim Level: By ensuring each claim within a long-form output is factually accurate using calibration techniques.
2. Overall Output Level: By applying conformal prediction techniques to provide high-probability guarantees that the entire set of generated claims is correct.

Moreover, the paper extends these techniques to handle multiple groups of prompts to ensure uncertainty estimates are valid across both the entire dataset and subgroups of interest, thereby addressing biases that may exist within specific subpopulations.

Methodology

Calibration

Calibration aligns the confidence scores generated by an LLM to the true likelihood of correctness. The authors utilize two primary methods:

• Histogram Binning (HB): Discretizes the output probabilities into bins and adjusts the outputs to better match the observed frequencies within these bins.
• Platt Scaling (PS): Uses logistic regression on the model's logits to produce calibrated probabilities.

To further refine these techniques, especially considering multiple groups, they introduce:

• Iterative Grouped Histogram Binning (IGHB): Iteratively corrects the calibration errors within each subgroup.
• Group Conditional Unbiased Logistic Regression (GCULR): Extends logistic regression to incorporate features from identified subgroups.

Conformal Prediction

Conformal prediction provides guarantees that a set of predictions is correct with a certain probability. The authors extend this through:

• Standard Conformal Prediction (SC): Constructs nested sets of claims ensuring marginal coverage.
• Conformalized Quantile Regression (CQR): Builds on linear quantile regression using pinball loss to minimize prediction errors.

The enhancements for subgroup analysis include:

• Multivalid Split Conformal (MVSC): Adjusts thresholds by iteratively addressing the group with the worst coverage error.
• Group Conditional Conformalized Quantile Regression (GCCQR): Incorporates group features in the linear quantile regression framework.

Empirical Evaluation

The empirical evaluation is conducted on biography generation tasks using two datasets: Bio-NQ (extracted from the Natural Questions dataset) and Bio-FActScore (entities used by prior work). The results demonstrate the efficacy of the proposed methods:

• Calibration: The multicalibrated methods (IGHB, GCULR) outperform their base counterparts (HB, PS) in terms of both average and maximum error across subgroups and overall dataset. This is evident from the improvements in ASCE and Brier scores.
• Conformal Prediction: The multivalid methods (MVSC, GCCQR) provide better subgroup coverage guarantees compared to standard methods, as indicated by the reduced mean coverage error across subgroups.

The evaluation highlights the practical benefits of considering subgroup features. Notably, even if subgroup fairness is not a primary concern, multicalibration yields better overall performance.

Implications and Future Directions

The methodological advancements proposed in this paper have significant theoretical and practical implications:

• Theoretical: The integration of multicalibration and multivalid conformal prediction frameworks enhances the robustness and bias mitigation capabilities of LLMs, addressing concerns over model fairness and reliability.
• Practical: Implementing these techniques in consumer-facing applications can improve user trust and the reliability of AI systems by transparently communicating the uncertainty of generated content.

Future developments can explore:

• Scalability: Enhancing the efficiency of multicalibration and multivalid methods to handle larger datasets and more complex models.
• Generalizability: Applying these methods to other long-form text generation tasks beyond biography generation.
• Human-in-the-loop Systems: Integrating these uncertainty quantification methods into interactive systems where human feedback can further refine model outputs.

The authors establish a benchmark for uncertainty quantification in long-form text generation, paving the way for enhanced, reliable, and fair LLM applications.