The conventional bibliographic retrieval systems are based on Boolean query formulations and inverted file implementations. Such systems provide rapid responses in answer to search queries but they are not easy to use by uninitiated patrons. An extended Boolean retrieval strategy has been devised in which the Boolean operators are treated more or less strictly, depending on the setting of a special parameter, known as the p-value. The extended system is much more forgiving than the conventional system, and provides better retrieval effectiveness. In this study various problems associated with the determination of appropriate p-values are discussed, and suggestions are made for an automatic assignment of p-values. Evaluation output is included to illustrate the operations of the suggested procedures.