Research On Polytomous Item Selection Strategy In CD-CAT

The item selection algorithm is a crucial element of CD-CAT,which makes the Cognitive Diagnostic Computerized Adaptive Testing(CD-CAT)tests have dynamic and adaptive characteristics.Although the dichotomous item selection algorithm has aroused great attention in CD-CAT,a few researches are on the polytomous items.This paper carried out three studies which related to the polytomous datas.At first,in study one,taking attribute balance into account.On the one hand,this paper proposed two kinds of improved polytomous item selection algorithm based on PSPWKL,which are VPWKL and VSPWKL.On the other hand,proposed 4 improved polytomous item selection algorithms based on the attribute discrimination index(ADI),which are SADI,VSADI,SADIKL and SADIPWKL.At the same time,improved AIDPWKL to polytomous directly and got ADIPWKL.Then,the experimental data was generated by R(3.6.2 version)and two simulation studies were carried out in this paper.In study two,the item bank was generated based on LC-DINA.Seven item selection algorithms were compared in attribute correct classification and item security with two existing methods PSKL and PSPWKL with the test length of 15,20 and 25.The simulation study shows that(1)In a whole,VSPWKL and VPWKL perform better than the algorithms that improved based on ADI.(2)VSPWKL and VPWKL are better than PSPWKL on attribute correct classification.(3)SADI is better than PSKL,while VSADI?SADIKL,SADIPWKL and ADIPWKL perform better than SADI.(4)Those seven algorithms are not so well performed as PSPWKL in item usage uniformity.In study three,VPWKL,VSPWKL and PSPWKL are used in mixed test,exploring the effects of different item administrated ratio and sequence on the test.The administrated sequences were set as follows: Sequence A(After all the polytomous items were administrated,then administrate the dichotomous items).Sequence B(At first,admministrate half of the dichotomous items.Then administrate all the polytomous items.Finally administrate the remaining dichotomous items.).Sequence C(After all the dichotomous items were administrated,then administrate the polytomous items).Sequence D(Administrate thepolytomous items randomly.).the item administrated ratio between polytomous and dichotomous items were set 2:3 and 3:2.The result show that(1)After all the dichotomous items were administrated,then administrate the polytomous items,the study got the lowest test accuracy and the worst item usage uniformity.But there's no uniform administrated sequence could guarantee that different item selection algorithms all have the highest accuracy.(2)“After all the polytomous items were administrated,then administrate the dichotomous items”,the item usage uniformity was the best.(3)When the item administrated ratio between polytomous and dichotomous items is 3:2,the test's result is more accurate.