IRS13 Scientific Report No. IRS-13 Information Storage and Retrieval Search Matching Functions 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. III-2~ Average (Mean) Concepts Per Documents 200 Documents 6o.6 153 DOCtSe that are 60.9 Sometimes Relevant h7 Docts. that are Always [OCRerr]o[OCRerr]-Relevant 59.7 Document length data for Cran-l Collection, using stem dictionary. Figure 13.