THE EFFECTS ON PARAMETER-ESTIMATION OF CORRELATED DIMENSIONS AND A DISTRIBUTION-RESTRICTED TRAIT IN A MULTIDIMENSIONAL ITEM RESPONSE MODEL

This study was designed to assess the effects on parameter estimation of correlated dimensions and a distribution-restricted trait on one di mension using a two-dimensional item response theory model. Multidimen sional analysis of simulated two-dimensional item response data fittin g a multidimensional two-parameter logistic item response theory model (McKinley & Reckase, 1983a; Reckase & McKinley, 1991) was done using the program MIRTE (Carlson, 1987). Six datasets (2 trait distributions X 3 levels of correlation between dimensions) of 2,000 trait vectors over 104 items were generated. Each dataset was analyzed and replicate d 100 times. Trait and item parameters generally were recovered adequa tely in the datasets in which both traits were normally distributed ov er the full range. In the datasets with a restricted range of trait le vel on the second dimension, recovery of the trait and item parameters was affected adversely. The results indicated that MIRTE recovers the structure of a multidimensional correlated space better than reported in earlier studies, especially when items are multidimensional.