Evaluating Health Question Answering Under Readability-Controlled Style Perturbations

AbstractPatients often ask semantically similar medical questions in linguistically diverse ways that vary in readability tone and background knowledge. A robust question answering QA system should both provide semantically consistent answers across stylistic differences and adapt its response style to match the users input however existing QA evaluations rarely test this capability creating critical gaps in QA evaluation that undermine accessibility and health literacy. We introduce SPQA an evaluation framework and benchmark that applies controlled stylistic perturbations to consumer health questions while preserving semantic intent then measures how model answers change across correctness completeness coherence fluency and linguistic adaptability using a human-validated LLM-based judge. The style axes include reading level formality and patient background knowledge all perturbations are grounded in human annotations to ensure fidelity and alignment with human judgments. Our contributions include a readability-aware evaluation methodology a style-diverse benchmark with human-grounded perturbations and an automated evaluation pipeline validated against expert judgments. Evaluation results across multiple health QA models indicate that stylistic perturbations lead to measurable performance degradation even when semantic intent is preserved during perturbation. The largest performance drops occur in answer correctness and completeness while models also show limited ability to adapt their style to match the input. These findings underscore the risk of inequitable information delivery and highlight the need for accessibility-aware QA evaluation.