The Influence of Anchor' Parameter Specification in IRT True Score Test Equating

Anchor is the most important fact in equating.In the nonequivalent groups with an anchor design, anchor affects the result of equating,and it is concerning with the construction of item bank.Basing on the data of HSK,This paper explores the influence of anchor size,anchor context and parameter specification in IRT true score equating.The result shows that anchor size and item context are not the key elements in equating.The error of equating does't decrease much with the increasing of anchor size;The error of equating is in relation with anchors parameter specification,the anchors using in IRT equating with high difficulty and discrimination, the more robust equating result will be gotten.