Assessing the Dimensionality of NAEP Reading Data

The reading data from the 1983–84 National Assessment of Educational Progress survey were scaled using a unidimensional item response theory model. To determine whether the responses to the reading items were consistent with unidimensionality, the full-information factor analysis method developed by Bock and associates (1985) and Rosenbaum's (1984) test of unidimensionality, conditional (local) independence, and monotonicity were applied. Full-information factor analysis involves the assumption of a particular item response function; the number of latent variables required to obtain a reasonable fit to the data is then determined. The Rosenbaum method provides a test of the more general hypothesis that the data can be represented by a model characterized by unidimensionality, conditional independence, and monotonicity. Results of both methods indicated that the reading items could be regarded as measures of a single dimension. Simulation studies were conducted to investigate the impact of balanced incomplete block (BIB) spiraling, used in NAEP to assign items to students, on methods of dimensionality assessment. In general, conclusions about dimensionality were the same for BIB-spiraled data as for complete data.