CRANV2 Conclusions chapter 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. - 260 - ".made up of four terms A, B, C and D, each of which have been used five times in the indexing of a set of documents as follows (x represents any other term or terms also used in indexing the documents): Document Index Number Terms 1 ADx 2 x 3 ACx 4 x 5 BCDx 6 x 7 Bx 8 x 9 ABCDx i0 x l i BDx 12 x 13 Ax 14 x 15 BCDx 16 x 17 Cx 18 x 19 Ax 20 x Searches for any combination of A, B, C and D would result in retrieval at various coordination levels as follows: Coordination Level No. of Documents Retrieved 4 1 (Document 9) 3 3 (Document 9, 5, 15) 2 6 (Document 9, 5, 15, i, 3, 1 10 (Document 9, 5, 15, 1, 3, 7, 13, 17, 19) 11) ii The particular significance of this point is the effect on retrieval performance of enlarging the classes. Assume that the search terms are broadened by being grouped with a related term, A1, B1. C1 or D1, and that these related terms have also each been used five times in the same set of 20 documents, the indexing being as follows: Thus the sum of the retrievals (1+3+6+10=20) is the same as the total number of postings for the four terms.