matched-control protocol

Separating Semantic Competition from Context Length in RAG Reading

This paper introduces a matched-control protocol to isolate whether RAG reader failures stem from context length or semantic competition among retrieved passages. By replacing hard-competitor passages with less competitive ones while holding passage count and length fixed, the authors demonstrate a measurable competition effect on SQuAD using Phi-2 and Qwen2.5-1.5B. Phi-2 recovers +6.0 EM and +7.0 answer-inclusion points; Qwen2.5-1.5B recovers +4.5 EM and +9.0 answer-inclusion points. The study also introduces retention curves and a right-censored half-life metric to track performance degradation as competitors accumulate.