Collection Overlap Analysis

Collection overlap analysis measures the degree to which two or more library collections hold the same titles, quantifying how much of each collection is shared, how much is unique, and how much in total the collections cover together. By treating holdings as sets and computing intersection, union, and overlap coefficients on matched identifiers such as ISBN, ISSN, or OCLC number, the method turns a vague sense of duplication into reproducible figures. These figures drive concrete decisions: where consortial partners can rely on one another, which titles are uniquely held and so must be preserved, and where duplicate purchasing or storage can be reduced. The technique is a workhorse of cooperative collection development and shared-print retention, summarized across the serials and collection-management literature including Nisonger's syntheses.