A procedure for assessing content-area and total-test dimensionality which uses response function discrepancies (RFD) was studied. Three different versions of the RFD procedure were compared to Bejar's principal axis content-area procedure and Indow and Samejima's exploratory factor analytic technique. The procedures were compared in terms of the consistency of decisions concerning dimensionality, and the amount of detail concerning content-area dimensionality which is available with each procedure. Achievement test data were from two multiple choice tests administered to over 2000 elementary school students in the Portland (Oregon) Public School system. One test contained 55 mathematics skill items and the other, 44 reading skill items. Results indicated that exploratory factor analysis provided a more global view of dimensionality; it was most likely to indicate that multidimensionality existed in the item responses, independent of the different content areas. The principal axis procedure tended to indicate more content-area multidimensionality. The RFD procedure was shown to be a viable method of determining response dimensionality, yet no single variation was consistently more informative. (GDC)