Automatic term mismatch diagnosis for selective query expansion

People are seldom aware that their search queries frequently mismatch a majority of the relevant documents. This may not be a big problem for topics with a large and diverse set of relevant documents, but would largely increase the chance of search failure for less popular search needs. We aim to address the mismatch problem by developing accurate and simple queries that require minimal effort to construct. This is achieved by targeting retrieval interventions at the query terms that are likely to mismatch relevant documents. For a given topic, the proportion of relevant documents that do not contain a term measures the probability for the term to mismatch relevant documents, or the term mismatch probability. Recent research demonstrates that this probability can be estimated reliably prior to retrieval. Typically, it is used in probabilistic retrieval models to provide query dependent term weights. This paper develops a new use: Automatic diagnosis of term mismatch. A search engine can use the diagnosis to suggest manual query reformulation, guide interactive query expansion, guide automatic query expansion, or motivate other responses. The research described here uses the diagnosis to guide interactive query expansion, and create Boolean conjunctive normal form (CNF) structured queries that selectively expand 'problem' query terms while leaving the rest of the query untouched. Experiments with TREC Ad-hoc and Legal Track datasets demonstrate that with high quality manual expansion, this diagnostic approach can reduce user effort by 33%, and produce simple and effective structured queries that surpass their bag of word counterparts.