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. Stem(s) versus Thesaurus(t) Input, Matching Function Precision at Recall Normalized No. Collection and Thesaurus Type .2 .5 .8 Rec. Pre. 20 Title, Cosine Numeric, Thes-l [] 21 Title, Cosine Numeric, Thes-SAl S T T T T 22 ADI Text, Cosine Logical, Thes-l S []S S T S 23 35 Text, Cosine Logical, Thes-SAl [[OCRerr] S 24 Requests Abstract, Cosine Logical, Thes-l T T T T 25 (contd) Text, Overlap Logical, Thes-l fls S []S 26 Text, Overlap Logical, Thes-SAl [[OCRerr]] 27 Abstract, Overlap Logical, Thes-l T S T T T The difference of one dictionary merit over the other is [OCRerr]ller than 0.05 when a letter alone appears, and larger than 0.05 when letters are circled. Table Summarizing 18 Precision Versus Recall Plots not Presented, Comparing Stem and Thesaurus Dictionaries on Three Collections Fig. 17 (continued)