Psychometric properties of the Friedreich Ataxia Rating Scale

Abstract

Objective To investigate the psychometric properties of the Friedreich Ataxia Rating Scale neurologic examination (FARSn) and its subscores, as well as the influence of the modifications resulting in the now widely used modified FARS (mFARS) examination. Methods Based on cross-sectional FARS data from the FA–Clinical Outcome Measures cohort, we conducted correlation-based psychometric analyses to investigate the interplay of items and subscores within the FARSn/mFARS constructs. Results The results provide support for both the FARSn and the mFARS constructs, as well as individually for their upper limb and lower limb coordination components. The omission of the peripheral nervous system subscore (D) and 2 items of the bulbar subscore (A) in the mFARS strengthens the overall construct compared with the complete FARS. Conclusions A correlation-based psychometric analysis of the neurologic FARSn score justifies the overall validity of the scale. In addition, omission of items of limited functional significance as created in the mFARS improves the features of the measures. Such information is crucial to the ongoing application of the mFARS in natural history studies and clinical trials. Additional analyses of longitudinal changes will be necessary to fully ascertain its utility, especially in nonambulant patients. ADL= : activities of daily living; CTT= : classical test theory; FA-COMS= : Friedreich Ataxia–Clinical Outcome Measures Study; FARS= : Friedreich Ataxia Rating Scale; FARSn= : FARS neurologic examination; FDS= : functional disability staging; FRDA= : Friedreich ataxia; ICARS= : International Cooperative Ataxia Rating Scale; IRT= : Item Response Theory; mFARS= : modified FARS; PCA= : principal component analysis; SARA= : Scale for the Assessment and Rating of Ataxia