Essays on Item Response Theory

Over the past three decades, since the publishing of Lord and Novick's Sta tistical Theories of Mental Test Scores in 1968 and Fischer's Einfiihrung in die Theorie psychologischer Tests in 1974, item response theory (IRT) has developed rapidly. This is demonstrated in the Handbook of Modern Item Response Theory (Van der Linden & Hambleton, 1997) with chapters on a wide range of topics in IRT. The study of individual responses to behavioral stimuli has clearly evolved into a major discipline of psychometric theory. The Dutch statistician and psychometrician Ivo Molenaar has played an important role in the growth of IRT, not only in the Netherlands but world wide. His contributions to item response modeling cover a broad area: item and person fit in both parametric and nonparametric models, for example, and polytomous nonparametric item response models including the devel opment of the MSP program. With Gerhard Fischer he edited a book on Rasch models that was published in 1995, and in cooperation with Klaas Sijtsma he is now preparing a textbook on nonparametric item response theory. In the Netherlands in particular, he has encouraged researchers and doctoral students to advance into new areas of IRT. To honor such achievements we dedicate this volume on item response modeling to Ivo W. Molenaar.