In this paper, data of almost 8 million loans of books recorded for 15 years by the Korea University Library are analyzed by using big data analytic techniques. During this period, book circulation decreased with an average annual rate of decline of 4.4%. The use factor of books in each Dewey decimal classification (DDC) class was evaluated to measure how efficiently books were used by library users. Loan frequencies of books were analyzed and meaningful results regarding loan concentrations

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... the half-lives of books were obtained. It was observed that 50% of the total loans in each year were for 20% of all borrowed books in that year. This phenomenon will be called the 20/50 loan rule, and the set of the top 20% most borrowed books, whose cumulative loan frequencies reach 50% of total loans, will be called a core collection. The 20/50 loan rule shows the loan concentration of library books. The extent of loan concentration gets stronger if loans for two or more consecutive years are concerned. It was found that with high probability, books in a core collection at a specific year are also categorized as a core collection in next years. Moreover, books categorized as a core collection in consecutive years have longer half-lives compared with all other circulating books.