How do you compare IR systems?

To compare information retrieval (IR) systems effectively, developers typically rely on three main approaches: standardized metrics, established test collections, and user-centered evaluations. Each method addresses different aspects of system performance, such as relevance accuracy, scalability, and real-world usability. Combining these approaches provides a comprehensive view of how well an IR system meets specific requirements.

First, standardized metrics like precision, recall, Mean Average Precision (MAP), and Normalized Discounted Cumulative Gain (NDCG) quantify relevance and ranking quality. Precision measures the fraction of retrieved documents that are relevant (e.g., if 8 out of 10 search results are useful, precision is 0.8). Recall calculates the fraction of all relevant documents retrieved (e.g., if a system finds 50 of 100 relevant documents, recall is 0.5). MAP averages precision across multiple queries, emphasizing ranking order, while NDCG penalizes systems that place relevant documents lower in rankings. For instance, a search engine optimizing for MAP might prioritize ranking the most relevant article first, while one using NDCG would ensure highly relevant items appear near the top even in longer result lists.

Second, test collections like TREC, Cranfield, or MS MARCO provide standardized datasets with queries, documents, and relevance judgments. These collections allow developers to benchmark systems under consistent conditions. For example, TREC’s ad-hoc retrieval tasks include curated queries and human-labeled relevance assessments, enabling direct comparison of algorithms. Developers might split a collection into training and test sets to evaluate how well a system generalizes. A system trained on TREC’s Robust04 dataset, which includes news articles, could be tested on its ability to retrieve relevant documents for unseen queries, ensuring results aren’t overfitted to specific data.

Third, user-centered evaluations measure real-world effectiveness through A/B testing or controlled experiments. Metrics like click-through rates, time-to-task-completion, or user satisfaction surveys reveal how actual users interact with the system. For example, an e-commerce platform might A/B test two search algorithms by measuring which leads to more purchases or fewer abandoned carts. In lab settings, developers might ask users to complete specific tasks (e.g., “Find a study on climate change published after 2020”) and track success rates or qualitative feedback. These tests highlight usability gaps that pure metric-based evaluations might miss, such as interface design flaws or mismatched user intent.

By combining quantitative metrics, standardized benchmarks, and user feedback, developers can holistically assess IR systems, balancing technical performance with practical usability.