Psychometric properties of the Berg balance scale in idiopathic Parkinson' disease in the drug off-phase.

BACKGROUND: Having an appropriate tool for assessment of the balance status during the drug off-phase in idiopathic Parkinson's disease (PD) is relevant for clinical and research settings. Our objective was to assess the clinimetric properties of the Berg balance scale (BBS) during drug off-phase in PD.

METHOD: Balance of 98 PD patients (mean age ± SD, 59.19 ± 10.88 years) was evaluated with the BBS. Other assessments in the study included the Fall Efficacy Scale-International (FES-I), Functional Reach Test (FRT), Section II of the Unified Parkinson's Disease Rating Scale-3.0, Parkinson's Disease Questionnaire-39 (PDQ-39), and Schwab and England Activities of Daily Living Scale. All evaluations took place during the drug off-phase. Internal consistency and inter- and intra-rater reliability were evaluated by Cronbach's alpha coefficient and intraclass correlation coefficient, respectively. Dimensionality was explored by factor analysis. Discriminative validity was tested by comparing BBS score between PD patients with and without a history of falling.

RESULTS: Internal consistency was high (α = 0.98), as were intra- and inter-rater reliability (ICC = 0.98 and 0.95, respectively). Factor analysis identified only one dimension for the BBS, whose convergent validity with FES-I, FRT, and domain mobility of the PDQ-39 were moderate or high (rS  = |0.60-0.74|). Correlation of BBS with functional scales and PDQ-39 Summary Index was moderate (rS  = |0.45-0.62|). Finally, the BBS showed a moderate strength to discriminate between PD patients with and without a history of falling.

CONCLUSION: Our study suggests that BBS has satisfactory internal consistency, reliability, and construct validity for measuring functional balance in people with PD during the drug off-phase.