Retrieval Models versus Retrievability

Retrievability is an important measure in information retrieval that can be used to analyze retrieval models and document collections. Rather than just focusing on a set of few documents that are given in the form of relevance judgments, retrievability examines what is retrieved, how frequently it is retrieved, and how much effort is needed to retrieve it. Such a measure is of particular interest within the recall oriented retrieval systems (e.g. patent or legal retrieval), because in this context a document needs to be retrieved before it can be judged for relevance. If a retrieval model makes some patents hard to find, patent searchers could miss relevant documents just because of the bias of the retrieval model. In this chapter we explain the concept of retrievability in information retrieval. We also explain how it can be estimated and how it can be used for analysing a retrieval bias of retrieval models. We also show how retrievability relates to effectiveness by analysing the relationship between retrievability and effectiveness measures and how the retrievability measure can be used to improve effectiveness. Shariq Bashir Department of Computer Science Mohammad Ali Jinnah University, Islamabad e-mail: [email protected] Andreas Rauber Institute of Software Technology and Interactive Systems TU Wien e-mail: [email protected]