Examination of the UPDRS bradykinesia subscale: equivalence, reliability and validity

Administering items or subscales separately from the measure for which they were designed to be a part may have unintended consequences for research and practice in Parkinson's disease (PD). The current study tested the equivalence of the bradykinesia subscale when administered alone versus as a component of the full 14-item Unified Parkinson's Disease Rating Scale (UPDRS) motor examination, as well as examined the reliability and validity of the bradykinesia subscale. The study sample consisted of 112 patients with PD. Patients were randomly assigned to either the bradykinesia subscale alone group (n = 56), who were administered the bradykinesia subscale separately from the rest of the UPDRS motor examination, or the full scale group (n = 56), who were administered the UPDRS motor examination in its standard format. The two one-sided t-test (TOST) procedure was used to test for mean equivalency between the two administration groups. Additionally, reliability and validity analyses were performed. The bradykinesia subscale mean scores from the full scale group and the subscale alone group were not statistically equivalent. However, in both groups, the bradykinesia subscale had exceptional reliability and was strongly and similarly related to age, activities of daily living, disability, and other assessments of motor symptom severity. The bradykinesia subscale is a valid and reliable assessment when administered separately from the rest of the UPDRS motor examination; however, caution should be taken when comparing mean scores across studies or occasions when different administrations are used.