Building an optimally-sized core collection by the Trueswell method

Abstract

Using the simple and ingenious statistical method developed by the American librarian it can be established what percentage of the existing holding should be used to deliver a given proportion of document requcsts. The optimal size of a core collection corresponding to 95-99,5 per cent of usage can be determined with satisfactory accuracy, and this part of document holding can easily be separated from the rarely used part of the holding by the shelf-time (the period between the two last loans). The method is illustrated by a survey conducted in the central branch of the Ervin Szabó Library in Budapest, and its application possibilities are discussed, including removal from and transfer of holding, comparison of similar libraries, quality improvement of acquisition, conversions, strategic planning.