440	 Record Linkage	 Special difficulties are encountered in devising reliable systems for searching and updating any large files of documents that must be identified primarily on the basis of names and other personal particulars. The underlying problem is that of making nearly maximum use of items of identifying information that are individually unreliable but that may collectively be of considerable discriminating power. Rules that can be applied generally to name retrieval systems have been developed in a methodological study of the linkage of vital and health records into family groupings for demographic research purposes. These rules are described and the ways in which information utilization for matching may be optimized are discussed.
