Construct Validity of the Observable Movement Quality Scale in Pediatrics: Hypothesis Testing of a Formative Measurement Model

BACKGROUND: The Observable Movement Quality (OMQ) Scale measures generic movement quality. Each item of the OMQ Scale focuses on a different element; together, the 15 items assess the whole construct of movement quality. OBJECTIVE: The aim of this study was to determine the construct validity of the OMQ Scale using 7 hypotheses defined to conform to the Consensus-Based Standards for the Selection of Health Measurement Instruments. DESIGN: This was an exploratory validation study. METHODS: A pediatric physical therapist assessed motor performance in 101 children using an age-specific motor test and the OMQ Scale. The direction, magnitude, and rationale for 7 hypotheses, which concerned relationships (n = 2), probability of low scores (n = 4), and difference between diagnosis subgroups (n = 1), were defined. RESULTS: The results confirmed 6 of the 7 hypotheses, indicating sufficient construct validity. Significant positive relationships were found between OMQ Scale total scores and the severity of motor disabilities (r = 0.72) and z scores on motor tests (r = 0.60). Probabilities for low scores on OMQ Scale items—exceeding the chi-square critical value—were confirmed for children diagnosed with spasticity, psychomotor retardation, mitochondrial diseases, and ataxia; however, probabilities for low OMQ Scale item scores on strength regulation in children with ataxia were not confirmed. OMQ Scale total scores for children who were not ambulatory because of neurological conditions were significantly different from those for children who were not ambulatory because of fatigue (r = 0.66). LIMITATIONS: The sample of children was based on theoretical assumptions about relevant variations in clinical representations; on the basis of the results, it appears that children with low strength regulation were underrepresented. CONCLUSION: The confirmation of nearly all hypotheses supported the validity of the OMQ Scale for measuring movement quality in clinical practice in addition to standardized age-adequate motor performance tests.