Abstract
MOKSCAL is a program for the Mokken (1971) scale analysis based on a nonparametric item response model (Mokken & Lewis, 1982) that makes no assumption about the functional form of the item trace lines. The only constraint the Mokken model puts on the item trace lines is the assumption of double monotony; that is, the set of scalable items must have the properties of monotonicity in item difficulties and nondecreasing item trace lines implying a monotone relation between the item success probabilities and the latent trait (Sytsma & Molenaar, 1987). MOKSCAL tests this assumption.
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