A procedure for estimating the degree to which a subtest uniquely contributes to total test performance is presented and discussed. Uniqueness analysis may be appropriately applied to any composite measurement instrument such as a multipart test or a multitest battery to assess the unique contribution of each component to the total test. The presentation in this report is in terms of the applicability of these procedures to Test 500 of the Professional and Administrative Career Examination. Uniqueness analyses were conducted on each series of Test 500 administered competitively in FY 75. The results for each of the five subtests, showing the degree to which subtest variance can be attributed to error, overlap, and unique sources, and indicating the potential unique validity of each subtest are presented by test series. (Author)