| Abstract: | For the fixed-effects three-parameter logistic model in item response theory, the necessary and sufficient condition of the model identification is presented synthesizing known results. An optimal transformation of parameters for model identification in Maris's unidentified case to remove or reduce the skewness of abilities is shown. In many cases, the vanishing skewnesses are obtained in the possible range of transformation for parameters with some improvements in the test response and information functions. |
