Search term combinations and retrieval overlap: A proposed methodology and case study

This article introduces a new methodology for studying the effects of term selection and postings overlap on retrieval, under the assumption that pooling results for several searchers or questions—an approach often used in conventional research in online searching—may obscure or eliminate important relationships. The proposed methodology involves comprehensive quantitative analyses, based on the concept of elementary postings sets, to be performed on combinations of search terms and postings sets for a single online search. Definitions for the Overlap(i, j) between two search terms and the global OverlapF for a search facet are proposed and evaluated. The methodology is tested for a particular case study, and is found to suggest insights not previously observed. Among the tentative findings are an understanding of why briefsearches cannot achieve high recall; that postings overlap data among terms in a facet can be used to flag and help one understand the semantic difference between single‐meaning and multi‐meaning facets; that for single‐meaning facets overlap among search terms in records is directly related to probability of relevance; that there is a fairly strong inverse relationship between the precision and the size of a postings set; and that a diminishing returns effect will ordinarily take place as additional search terms are added to a facet. Implications of these ideas for searching are discussed, and an algorithm for traversing a most rational path during the search process is proposed. Several tentative conclusions and hypotheses are posited, and suggestions for future research are offered. © 1990 John Wiley & Sons, Inc.