Abstract:

A testlet is a cluster of items that share a common passage, stimulus, or other context, and the dependence between testlet-based item responses that caused by the common stimulus called testlet effect. This article introduced and combed the concepts of testlet, local independence and local dependence, and proposed the concepts of testlet effect in accordance with previous research. Applying standard item response models to testlet responses leaded to many problems such as biased parameter estimation and overestimation of test reliability, hence, testlet response model was introduced to deal with testlet effect better. 6 testlet response models were described in detail including Higher-order testlet model and Multilevel testlet model, and two issues were discussed: (a) the connotation of slope parameter in testlet response model is different from that in standard item response theory which is inappropriate to contrast the two directly; (b) testlet response model belongs to general multidimensional item response model and the main distinction with special multidimensional item response model is the latent factors needed to control to satisfy general local dependence hypothesis.

Key words: testlet response theory, testlet response model, multidimensional item response theory, general multidimensional item response model, general local independence