A is for Adele: An Offline Evaluation Metric for Instant Search

Instant search has emerged as the dominant search paradigm in entity-focused search applications, including search on Apple Music, Kayak, LinkedIn, and Spotify. Unlike the traditional search paradigm, in which users fully issue their query and then the system performs a retrieval round, instant search delivers a new result page with every keystroke. Despite the increasing prevalence of instant search, evaluation methodologies for instant search have not been fully developed and validated. As a result, we have no established evaluation metrics to measure improvements to instant search, and instant search systems still share offline evaluation metrics with traditional search systems. In this work, we first highlight critical differences between traditional search and instant search from an evaluation perspective. We then consider the difficulties of employing offline evaluation metrics designed for the traditional search paradigm to assess the effectiveness of instant search. Finally, we propose a new offline evaluation metric based on the unique characteristics of instant search. To demonstrate the utility of our metric, we conduct experiments across two very different platforms employing instant search: A commercial audio streaming platform and Wikipedia.