Objective: To determine the structural validity, reliability, and minimally important difference values for the SCOPA-AUT.

Background: Autonomic dysfunction is common in Parkinson’s disease (PD). A commonly used self-report, outcome measure recommended by the MDS is the SCOPA-AUT. Its proposed subscales have not been subject to independent validation. Additionally, the long-term test-retest reliability and minimally important difference are unknown and needed to adjudicate meaningful change.

Method: Baseline Parkinson’s Progression Markers Initiative participants who completed the SCOPA-AUT included 4,450 individuals who were mostly older (M_age=65.2, SD=8.7) men (54.3%), with a subset returning at one year. The 25 items capture cardiovascular, gastrointestinal, urinary, thermoregulatory, pupillomotor, and sexual autonomic symptoms. Exploratory factor analyses (EFA) using ordinary least squares estimation with oblimin rotation were conducted on a random 20% of the sample. The remaining 80% served to cross-validate with confirmatory factor analyses (CFA) using ordinal estimation and confirmatory fit index, Tucker-Lewis index, standardized root mean square residual, and root mean square error of approximation. McDonald’s omega quantified internal consistency and intraclass correlations marked test-retest at one-year.

Results: EFAs suggested one-, two- (urinary & dysautonomia), five- (published structure), and six- (published structure with GI being split into upper and lower signs) factor models. CFAs indicated that the six-factor model had the best fit, and the published model had marginal fit, whereas the one and two factor models were insufficient. We found adequate internal consistency for the published and modified subscales (ωs=.64-.79) and total score (ω=.84). There was strong, one-year, test-retest consistency for all participants (ICC=.88) and controls (ICC=.82); the latter were used to calculate minimal change values of ≥5 or ≥7 depending on level of certainty.

Conclusion: The SCOPA-AUT has good evidence for use of published subscales, although a modification of the GI scale is indicated. Additionally, we established the minimally important difference to determine reliable response in clinic and trials.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/structural-validity-reliability-and-minimally-important-differences-for-the-scopa-aut/