Assessing Local Dependence in Educational Performance ...

As,~,sinll Local l:~dmno=. 13DiscussionOur description of the contents of the seven item clusters with substantial lcx~!dependence points to some likely causes of item interdepcndcnce and suggest ways toavoid it. For example, test developers probably should expect compare-contrast items to belocally dependent because contrasting two or more objcct~ probably requires attention totheir similarities. In addition, items that are inu:ntionally interdependent, like themathematics content items here in which responses to items are built on each othersequentially, are likely to produce statistical local dependence. Also, reasoning itemswhich require examinees to explain and justify previous responses are also likely to belocally dependcnc Finally, any items that require attention to given information -- forexample, reading passages and the data tables in the mathematics tasks in this stud,," -- arelikely to be locally dependent to some degree.Yen (in press), in a comprehensive examination of local item dependence using datafrom the Comprehensive Tests of Basic Skills (CTBS/4) and the 1991 edition of theMSPAP, the same performance assessment used in this study, presents a compendium ofpossible causes of item dependence. She refers to these causes as external assistance orinterference; speededness; fatigue; practice; item or response format; passage dependence;item chaining; explanation of previous answer; scoring rubric or raters; and content.knowledge, and abilities. Several of the possible causes in her list appear consistent withthose hypothesized in this study (i.e., passage dependence, item chaining, and explanationof previous answer). Other possible causes in her list (i.e., external assistance orinterference, speededness, fatigue, practice, scoring rubric or raters) would not beidentified by examining items, as was done in this study. The other two causes in her list(item or response format; scoring rubric or raters; and content, knowledge, and abilities)were not hypothesized in this study.