Psychometric Validation of the Modified Functional Scale for the Assessment and Rating of Ataxia (f-SARA) in Patients With Spinocerebellar Ataxia

Abstract

This study aimed to generate evidence to support psychometric validity of the modified functional Scale for the Assessment and Rating of Ataxia (f-SARA) among patients with spinocerebellar ataxia (SCA). Psychometric measurement properties and minimal change thresholds of the f-SARA were evaluated using data from a cohort of SCA subjects (recruited at Massachusetts General Hospital [MGH]; n = 33) and data from a phase 3 trial of troriluzole in adults with SCA (NCT03701399 [Study 206]; n = 217), including a subset of patients with the SCA3 genotype (n = 89). f-SARA item ceiling effects were absent within the MGH cohort, while floor effects were present. Excellent internal consistency reliability was demonstrated (αtotal = 0.90; αitems-removed = 0.86–0.90), and item-to-total correlations were strong (r = 0.82–0.91, per item). High test–retest reliability was demonstrated with intraclass correlation coefficients of 0.91 (total) and 0.73–0.92 (items). Convergent and divergent validity was supported, with strong correlations observed between the f-SARA and similarly constructed scales (FARS-FUNC, BARS, PROM-ADL, and FARS-ADL; all p < 0.001) and weaker correlations observed among measures of differing constructs. Mean item and total scores increased with disease severity (by FARS-FUNC quartile; p < 0.001). A 1-point threshold for meaningful changes was supported as 0.5 × SD = 0.89, SEM = 1.12, and mean changes from baseline for patients classified as “improved,” “no change,” or “deteriorated” were −0.68, 0.02, and 0.58, respectively. Similar trends were observed in Study 206 all-SCA and SCA3 cohorts. The measurement properties of the f-SARA provide evidence of its psychometric validity, responsiveness, and suitability as a clinical outcome measure in patients with SCA, including those with SCA3.