CRANV2 summary summary Cyril Cleverdon Michael Keen Cranfield An investigation supported by a grant to Aslib by the National Science Foundation. Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. SUMMARY The test results are presented for a number of different index languages using various devices which affect recall or precision. Within the environ- ment of this test, it is shown that the best performance was obtained with the[OCRerr]group of eight index languages which used single terms. The group of fifteen index languages which were based on concepts gave the worst perform- ance, while a group of six index languages based on the Thesaurus of Engineering Terms of the Engineers Joint Council were intermediary. Of the single term index languages, the only method of improving performance was to group synonyms and word forms, and any broader groupings of terms depressed performance. The use of precision devices such as links gave no advantage as compared to the basic device of simple coordination. All results have to be considered within the context of the experimental environment, but they can be said to substantiate or clarify many of the findings of Cranfield I. It is conclusively shown that an inverse relationship exists between recall and precision, whatever the variable may be that is being changed. The ,two factors which appear most likely to affect perform- ance are the level of exhaustivity of indexing and the level of specificity of the terms in the index language. For any given operational situation, the optimum levels cannot be categorically stated in advance, but can only be determined by an evaluation of the system, the main consideration probably being the subject field. It would be unusual ff the characteristics of the subject field used for this test were such as to make it unique, so the high performance obtained with the single terms in natural language can be considered to be of some ir[OCRerr]portance in regard to the use of natural language text as input to mechanised systems.