Movement skill assessment in children with profound multiple disabilities: a psychometric analysis of the Top Down Motor Milestone Test

Abstract

Objective: To analyse the psychometric properties of the Top Down Motor Milestone Test (TDMMT), an internationally used instrument in the planning and evaluation of movement-oriented interventions. Setting: Centres for special education in the Netherlands. Subjects: Children with profound multiple disabilities. Methods: Validity, reliability and utility of the TDMMT were evaluated. Validity was assessed by conducting a principal component analysis. Reliability was determined by evaluating the internal consistency, test=retest and inter-rater reliability. With regard to utility, the hierarchical item ordering was evaluated with a Mokken scale analysis. Inter-item and item-rest correlations were calculated to confirm the allocation of the items in the TDMMT. Results: Principal component analysis did not support the presence of three underlying factors. The internal consistency was high and test=retest and inter-rater reliability varied from moderate to perfect. Scale analysis showed that the subscales of the TDMMT are strong one-dimensional scales with good internal consistency, however, the order of the items could only partly be confirmed as well as the allocation of the items into four levels of functioning. Conclusion: The reliability of the TDMMT is good, but validity is moderate. Results indicate that adaptations to the structure of the TDMMT should be made when used for children with profound multiple disabilities. Further psychometric evaluation of the TDMMT is necessary.