Abstract
The model of time-dependent distribution of books by their loan time has been seen as a useful tool for library management.，especially for book relegation. Quentin L. Burrell has proposed an excellent model of negative binomial distribution derived from a theory of stochastic process. However, the model does not fit the real observations. This paper shows it by using four-years circulation data of a Japanese university library，and tries to construct an alternative model by extending Burrell's model. The modified model incorporating a new idea obtained inductively from data proves to fit real observations well. The idea is to consider a parameter k of the negative binomial distribution as a time-dependent variable.
