Structural Validity of the Mini-Balance Evaluation Systems Test in Individuals With Spinocerebellar Ataxia: A Rasch Analysis Study

Abstract

Objective: To examine the structural validity of the Mini-Balance Evaluation Systems Test (Mini-BESTest) in individuals with spinocerebellar ataxia (SCA).

Design: Methodological research on data gathered in a cross-sectional study. A Rasch analysis was conducted (partial credit model).

Setting: Inpatients in a hospital rehabilitation setting.

Participants: A pooled sample of patients with SCA (N=65 [total 110 data]; 23 women, 42 men; mean±SD age 63.1±9.9y).

Interventions: Not applicable.

Main outcome measures: We evaluated the Mini-BESTest's category structure, unidimensionality, and measurement accuracy (0: unable to perform or requiring help to 2: normal performance).

Results: The Mini-BESTest rating scale fulfilled the category functioning criteria. The analysis of the standardized Rasch residuals showed the scale's unidimensionality, but there were 7 item pairs indicating local dependence. All of the items fit the underlying scale construct (dynamic balance), with the exception of item #1, "Sit to stand," which was an underfit. The Mini-BESTest demonstrated adequate reliability (person separation reliability=.87) and separated the patients into 5 strata. The item-difficulty measures ranged from -4.49 to 2.02 logits, and the person ability-item difficulty matching was very good (the mean of person ability=-.07 logits and the mean of item difficulty=.00). No floor or ceiling effects were detected. The keyform identified items with small (#11, "Walk with head turns, horizontal") and large (#3, "Stand on 1 leg") item thresholds.

Conclusions: The Mini-BESTest has a unidimensional balance assessment scale with good category structure and reliability even for individuals with SCA. However, it also has some inherent shortcomings such as fit statistics, local item dependencies, and item thresholds. The results obtained when the Mini-BESTest is administered to patients with cerebellar ataxia should, thus, be interpreted cautiously.

Keywords: Cerebellar ataxia; Postural balance; Psychometrics; Rehabilitation.