Improving Zero-Shot Ranking with Vespa Hybrid Search

Exploring the concept of zero-shot text ranking, this blog post examines how ranking models, particularly those using pre-trained neural language models like BERT, perform when applied to new domains without prior adaptation. The post introduces the BEIR benchmark, which evaluates the generalization of text ranking models across 18 diverse datasets with varying relevance judgments. Highlighted is the Dense Passage Retriever (DPR) model, which excels in in-domain settings but underperforms compared to the BM25 baseline in out-of-domain zero-shot scenarios, demonstrating that in-domain success does not guarantee out-of-domain effectiveness. This analysis underscores the necessity of evaluating retrieval methods on a wide range of datasets to ensure robust performance. The post also previews a forthcoming discussion on a hybrid ranking model combining multi-vector representations with BM25 to address the limitations of single-vector models in zero-shot settings.