On “Benka Wallén M, Sorjonen K, Löfgren N, Franzén E. Structural validity of the Mini-Balance Evaluation Systems Test (Mini-BESTest) in people with mild to moderate Parkinson disease.” Phys Ther. 2016;96:1799–1806.

Abstract

We read with attention the article by Benka Wallen et al.1 The aim of their study was to examine the dimensionality of the Mini-BESTest, as well as the properties of its items and their interrelationship, in a sample of elderly individuals with mild-to-moderate Parkinson disease (PD). New studies on the psychometric features of the tool in specific populations are welcome. In particular, the authors have interestingly emphasized the peculiarity of the Timed “Up & Go” Test with dual task (item 14) in the participants under study. In fact, this test may even be a sensitive predictor of early impairment in PD2 and merits further attention. However, we are concerned about some critical points related to both data processing and interpretation. Thus, we take this opportunity to highlight a series of sensitive issues that may have affected the results of both Rasch analysis and exploratory factor analysis (EFA) and propose additional analyses and comments on the data set in order to find more parsimonious and plausible explanations for some results. The authors attempted to replicate the calibration of the Mini-BESTest (an instrument aimed at measuring balance deficits) in a sample in which about half of the participants had mild to moderate balance deficits (Hoehn & Yahr stages 1–2, where, by definition, stage 2 means “bilateral or midline involvement without impairment of balance”) and none had severe or very severe balance deficits (ie, balance ability less than −1.5 logits, in their Fig. 1).1 In such a situation, any statistical analysis would tell you more about the specific characteristics of that sample than about the actual general performance of the tool used for balance measurement. Indeed, in a sample such as this one (not large), a reduced number of participants can provide useful (but only partial) information for the calibration …