Has Item Response Theory Increased the Validity of Achievement Test Scores?

It is clear that item response theory (IRT) has been the basis of many important contributions to educational measurement and has opened up a number of new possibilities such as adaptive and customized testing. The focus of this article, however, is on the question of the contribution of IRT to the validity of interpretations of achievement test results in the context of four specific applications: construction of scales for achievement tests; test construction; development of customized tests; and investigation of the influence of instruction on achievement tests. It is concluded that content considerations deserve greater attention in applications of IRT with achievement tests than they seem to have been given in these contexts.