THE 80/20 RULE: LIBRARY LORE OR STATISTICAL LAW?

It is shown that Trueswell's empirical 80/20 rule arises quite naturally, in general terms at least, from the type of stochastic model for library loans presented by Burrell and Cane. Particular attention is paid to previously suggested uses of the rule in identifying a ‘core collection’ for a library. This emphasizes that the length of the time period considered is of crucial importance.