PCQC: Privileged Counterfactual Question Credit for Multi-Turn Medical Dialogue

TL;DR - PCQC is a training method that assigns question-level credit in medical dialogues by evaluating both asked and counterfactual questions using privileged patient information. It improves diagnostic accuracy while requiring fewer inquiry turns than competing reinforcement-learning methods.

• Constructs answers to unasked alternative questions from privileged patient facts, avoiding full counterfactual dialogue rollouts.
• Uses a frozen diagnostic scorer to compare how strongly each question-answer pair supports the correct diagnosis.
• Combines relative question credit with outcome-based reinforcement learning to supervise executed and unexecuted questions.
• Achieves 63.10% mean accuracy across four benchmarks—4.38 points above GRPO and 4.21 above ATPO—with 33.1% fewer inquiry turns than GRPO.