The method of paired comparisons for recording human judgments has a long history, dating back at least to the late 19th century. An early English text on experimental psychology by Titchener (1901) covered paired comparisons, and Thurstone (1927a, 1927c) brought considerable attention to the method with his psychological scaling proposals in the late 1920's. Summaries of the method are found in psychometric textbooks (for example, Guilford 1954; Nunnally 1976; Torgerson 1958) and, from the statistical perspective, in the books by David (1988) and Bock and Jones (1968).