When I set out to evaluate retrieval configurations for Portuguese clinical text, I expected one method to dominate. Instead, I found something more interesting: BM25 and dense retrieval solve different questions. Neither is a substitute for the other.

This post summarizes the methodology and results from a 500-query empirical study of hybrid retrieval for clinical question answering. All code is open source: https://github.com/nomad-link-id/hybrid-rag-pipeline

The Setup

500 clinical queries across 6 medical specialties (cardiology, endocrinology, infectology, nephrology, neurology, oncology).…