Zuru Du, a graduate at this year's convocation, received the 1999 AERA Division D Mary Catherine Ellwein Outstanding Dissertation Award at April's AERA Conference for his dissertation Modeling Conditional Item Dependencies with a Three-Parameter Logistic Testlet Model. Two years ago, Du was awarded a summer research scholarship from the Educational Testing Service (ETS) in Princeton, New Jersey. At the time he said, "The work they are doing at ETS is directly related to my program. I think it will help me get a clear idea for the topic of my dissertation."

Du's dissertation looked at assumptions that are made in standard test models. He developed a new test model based on his findings and then wrote a computer program to implement that model.

"The previously existing models have a serious flaw," Du explained, "and the purpose of the new model is to fix that flaw." The flaw he refers to is that the standard testing models assume that an examinee's responses to any pair of items are statistically independent of each other. This assumption is untenable in many important situations, Du said.

"When we looked at currently used standardized educational tests, we found they often include groups of related items, such as tables or graphs followed by groups of questions relating to them," he said. "These groups of items share common stimuli. An examinee's responses to these items are not likely to be independent of each other."

Du did intensive research to come up with a new procedure. He then wrote a computer program to implement his methodology and tested the program by comparing the standard model against his new model. "It was shown that when tests include groups of related items, by using the new model, measurement efficiency can be improved by as much as 20 percent," Du said.

His research spawned a flurry of response from others in the field. ETS requested permission to use his computer program and will publish his entire dissertation in their research report series. ETS also awarded him a Postdoctoral Research Fellowship. Also, three professional journals, including Psychometrika, have asked him to review manuscripts in areas of his expertise.

Published Tuesday, Sep. 18, 2001