Latent trait analysis

Let us begin with a well known example. Figure la shows, in path diagram form, the intraclass correlation between alternate forms of a test, observed scores represented as boxes. As the diagram shows this correlation can be interpreted as representing the variance accounted for by the influence of the true score (T)—a latent trait shown in the circle (Hayes, 1973, p. 535). The rules of path analysis tell us that the correlation is made up of the sum of the multiplication of the terms of each path that connect the trait. Thus the equation ... 

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