Construct Validity of the Sensory Integration and Praxis Tests

The purpose of this study was to examine the construct validity of the praxis tests of the Sensory Integration and Praxis Tests (SIPT) and to determine whether the practic component of sensory integration-based developmental dyspraxia is a unitary or a multidimensional disorder. Developmental dyspraxia is an impaired ability to plan and execute skilled or nonhabitual motor tasks; however, its underlying cause, or even whether praxis is a unitary or multidimensional function, is not yet clarified. In this study, the Rasch model of measurement (Linacre, 1989; Wright & Masters, 1982; Wright & Stone, 1979) was used to explore the underlying construct of developmental dyspraxia. The Rasch model was chosen because its use enabled us to (a) confirm goodness-of-fit of individual items within SIPT praxis tests and (b) examine the hierarchical structure of item difficulties. The data included the raw scores of the SIPT praxis tests of 210 subjects from Canada and the United States. The results of the Rasch analyses revealed that each of these five SIPT praxis tests measures a single, unidimensional construct. When the items from the five tests were combined to create a single 117-item test, the items continued to define a single practic function. This indicates that a unitary practic component underlies both bilateral integration and sequencing deficits and somatodyspraxia. Finally, examination of the hierarchy of item difficulties resulted in recommendations for the development of a single screening test for developmental dyspraxia. The implications of these results for clinical practice and future research are discussed.