Applications of Item Response Theory to Practical Testing Problems

Applications of Item Response Theory to Practical Testing Problems

Applications of Item Response Theory to Practical Testing Problems

Applications of Item Response Theory to Practical Testing Problems

Excerpt

This chapter is not a substitute for a course in classical test theory. On the contrary, some knowledge of classical theory is presumed. The purpose of this chapter is to provide some perspective on basic ideas that are fundamental to all subsequent work.

A psychological or educational test is a device for obtaining a sample of behavior. Usually the behavior is quantified in some way to obtain a numerical score. Such scores are tabulated and counted. Their relations to other variables of interest are studied empirically.

If the necessary relationships can be established empirically, the scores may then be used to predict some future behavior of the individuals tested. This is actuarial science. It can all be done without any special theory. On this basis, it is sometimes asserted from an operationalist viewpoint that there is no need for any deeper theory of test scores.

Two or more "parallel" forms of a published test are commonly produced. We usually find that a person obtains different scores on different test forms. How shall these be viewed?

Differences between scores on parallel forms administered at about the same time are usually not of much use for describing the individual tested. If we want a single score to describe his test performance, it is natural to average his scores across the test forms taken. For usual scoring methods, the result is effectively the same as if all forms administered had been combined and treated as a single test.

The individual's average score across test forms will usually be a better . . .

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