Relationship of Frequency and Information Quantity of Single KeywordsCHENG Li, WU Guang-yin, WANG Xin(Institute of Scientific and Technical Information of China,Beijing 100038,China)Abstract: This paper study the relationship between frequency and information quantity of single key⁃words both theoretically and empirically. We analysis the difference on demand expression of retrievalwords with different probabilistic. Research the crowding out effect of high frequency keywords to low fre⁃quency of keywords based on multidimensional description of information demand. Aiming at this effect,we provide a new relevant measurement program of retrieve in which before the calculate keywords will beclassified according to its relationships in the thesaurus.Key words: frequency of retrieval words; information quantity; dimension of Information needs; retrievalrelevance