Overlap Among the Journal Articles Selected for Coverage by BIOSIS, CAS, and Ei

Of 14, 592 primary journals being collectively monitored by the BioSciences Information Service of Biological Abstracts (BIOSIS), the Chemical Abstracts Service (CAS), and Engineering Index, Inc. (Ei) on 1 May 1970, only 4081 were being monitored by two or more of the services. The extent to which all three or any two of these services select the same journal article for coverage was determined by examining each service's selection records for the July 1969–June 1970 issues of these 4081 overlap journals. The maximum possible journal article overlap among BIOSIS, CAS and Ei was found to be 822 articles and between BIOSIS and Ei, 1428 articles. The journal article overlap between BIOSIS and CAS was found to be 48, 856 articles and between CAS and Ei, 21, 583 articles.