Document searching systems, such as those in libraries, are comprised of chains of components that transmit information. The components consist of mechanisms for doing classification, indexing, abstracting and cataloging of documents, and for converting users' statements of need to expressions suitable for searching the system. Improvement of the transmission fidelity of components requires that fidelity be measurable. The Pattern Congruity Method has been devised for accomplishing this. The method adapts paired-comparison judgment procedures from experimental psychology to the measuring of judgments of document content and the content of representations such as titles and abstracts. It provides a measure of agreement between different instances of the same component, such as between indexers, and also allows direct measurement of fidelity, i.e., the degree of correspondence or congruity between patterns of content of full documents and patterns as depicted by each component in the chain that transduces information about document contents. The method has been used to compare human and machine indexing products, to evaluate machine classification, to study conceptual structures underlying the use of indexing terms, and is currently being employed to study functional overlap in abstracting and indexing services. The method has been experimentally tested for two years under sponsorship of the National Science Foundation. (Author/JB)