Item Response Theory Scale Linking in NAEP

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In educational assessments, it is often necessary to compare the performance of groups of individuals who have been administered different forms of a test. If these groups are to be validly compared, all results need to be expressed on a common scale. When assessment results are to be reported using an item response theory (IRT) proficiency metric, as is done for the National Assessment of Educational Progress (NAEP), establishing a common metric becomes synonymous with expressing IRT item parameter estimates on a common scale. Procedures that accomplish this are referred to here as scale linking procedures. This chapter discusses the need for scale linking in NAEP and illustrates the specific procedures used to carry out the linking in the context of the major analyses conducted for the 1990 NAEP mathematics assessment.