Fair Representation in Parliamentary Summaries: Measuring and Mitigating Inclusion Bias

The use of Large language models (LLMs) to summarise parliamentary proceedings presents a promising means of increasing the accessibility of democratic processes. However, as these systems increasingly mediate access to political information, filtering and framing content before it reaches users, there are important fairness considerations to address. In this work, we evaluate 5 LLMs (both proprietary and open-weight) in the summarisation of plenary debates from the European Parliament to investigate the representational biases that emerge in this context. We develop an attribution-aware evaluation framework to measure speaker-level inclusion and (mis)representation in debate summaries. Across all models and experiments, we find that speakers are less accurately represented in the final summary on the basis of (i) their position in the speaking-order (speeches in the middle of the debate were systematically excluded), (ii) the language spoken (non-English speakers were less faithfully represented), and (iii) their political affiliations (better outcomes for left-of-centre parties). We further show how biases in these contexts can be decomposed to distinguish inclusion bias (systematic omission) from hallucination bias (systematic misrepresentation), and explore the effect of different mitigation strategies. Prompting strategies do not affect these biases. Instead, we propose a hierarchical summarisation method that decomposes the task into simpler extraction and aggregation steps, which we show significantly improves the positional/speaking-order bias across all models. Critically, we find that language and partisan biases persist, indicating that architectural interventions are unlikely to solve biases that emerge due to bias or imbalance in the training data. These findings underscore the need for domain-sensitive evaluation metrics and ethical oversight in the deployment of LLMs for multilingual democratic applications.