This study was designed to explore the practicality, flexibility, reliability, and sensitivity of the Criterion Group Method of measuring the effectiveness and efficiency of indexing, a method using a criterion group to set the standard for "ideal" indexing. These major variables were examined: (1) size of document sample, (2) size of Criterion Group, (3) instructions to indexers and use of a vocabulary guide, (4) three methods of editing raw indicia to make terms comparable, and (5) two methods of weighting indexers' scores. Scores earned by a set of eight professional indexers, by individual authors of the test documents and, in some cases, scores for title sets or medical students' indexing were compared within selected treatments to measure the extent to which the detectability of differences was achieved by each treatment. A two-way analysis of variance was used to relate reliability of test scores to document sample size and criterion group size. From the results of these studies of the methodologic variables, it was concluded that the criterion group method of evaluating indexing can be a practical yardstick for a wide variety of managerial, research, and educational uses. Appendixes include the rationale of the method, a literature review, information on materials employed and subjects participating in study trials, and details on manual and computer implementation. (Author/JB)