IRS13 Thesaurus, Phrase and Hierarchy Dictionaries chapter E. M. Keen Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. 0 ½ A ½ A STEM THESAURUS- (OLD Q. S.) 0 ¼ ½ REC SION PRECISION 1.0 - I.c - QB 0.8 A 0.6 - 0.6 - 0[OCRerr]A[OCRerr] 0A 0.4 - \ [OCRerr]0 [OCRerr] OA - STEM THESAURUS-2(NEW Q.S.) 0.2 - 0.2 - I I I I i I I I I I[OCRerr]RECALL * I I i I I I I I I 1[OCRerr]RECALL 0 0.2 0.4 0.6 0.8 O[OCRerr] 0 1.2 0.4 0.6 0.8 I.[OCRerr] Comparison 12 Comparison 13 Cran-1, Indexing, 42 Requests Cran-1, Indexing, 42 Requests Performance Curves Comparing Stem and Thesaurus Dictionaries on the Cran-1 Indexing Collection Fig. 11