DOCUMENTATION NOTE: SIMPLE STOCHASTIC MODELS FOR LIBRARY LOANS

Quentin Burrell points out that the circulation distribution observed in several library collections is approximately geometric and seeks to explain this phenomenon. He selects one of a number of alternative explanations; that the items in the collection have different levels of ‘popularity’ and that the distribution of popularity is negative exponential: and that for a given popularity the number of borrowings in a time period has a poisson distribution. He proves that this combination does produce a geometric circulation distribution. Finally he introduces a zero‐use category of books which is used to explain the higher than expected number of books that are not borrowed at all in the data. However, alternative models also fit the data and his basic explanation does seem dubious in qualitative terms.