Two of the most popular methods for obtaining equal-interval scales for educational measurement are discussed: Thurstone's method and Item Response Theory (IRT). Between-grade growth on these scales is compared; while unstandardized differences show different trends for the two scales, standardized differences that take standard deviations into…

Unidimensional item response theory (IRT) is widely used in the analysis and equating of educational achievement tests. If an IRT model is true, item response must be locally independent when the trait is held constant. Several measures of local dependence which are used in conjunction with the three-parameter logistic model in the analysis of…

A procedure for obtaining maximum likelihood trait estimates from number-correct (NC) scores for the three-parameter logistic model is presented. It produces an NC score to trait estimate conversion table. Analyses in the estimated true score metric confirm the conclusions made in the trait metric. (Author/DWH)

Basic skills tests in which measurement of growth is defined in the context of national norms are discussed. An integral part of the construction of norms is the production of a trait or ability score which is normed. Test publishers define a multidimensional trait by including items which measure it. The trait as a construct is a distinct…