RESULTS OF FIFTY DIFFERENT RETRIEVAL METHODS AS APPLIED IN THREE EXPERIMENTAL RETRIEVAL SYSTEMS WERE SUBJECTED TO AN ANALYSIS SUGGESTED BY STATISTICAL DECISION THEORY. THE ANALYSIS USES A PREVIOUSLY-PROPOSED MEASURE OF EFFECTIVENESS AND DEMONSTRATES ITS SEVERAL PROPERTIES. SOME OF THESE PROPERTIES ARE--(1) IT ENABLES THE RETRIEVAL SYSTEM TO DISTINGUISH BETWEEN WANTED AND UNWANTED ITEMS. (2) IT IS NOT CONFOUNDED BY THE RELATIVE WILLINGNESS OF THE SYSTEM TO OMIT ITEMS, (3) IT IS A SINGLE NUMBER, AND (4) IT ALLOWS THE COMPLETE ORDERING OF DIFFERENT PERFORMANCES. THE EXAMINATION OF A WIDE RANGE OF DATA IN RELATION TO THIS ONE MEASURE ALSO PROVIDES A GENERAL ASSESSMENT OF THE CURRENT STATE OF THE RETRIEVAL ART. THIS DOCUMENT IS AVAILABLE AS AD-656-340 FROM THE CLEARINGHOUSE FOR FEDERAL SCIENTIFIC AND TECHNICAL INFORMATION, SPRINGFIELD, VIRGINIA, 22151, $3.00 FOR HARD COPY, $0.65 FOR MICROFICHE, 52 PAGES. (AUTHOR/CM)