Psychometric properties of four fear of falling rating scales in people with Parkinson’s disease

BACKGROUND Fear of falling (FOF) is commonly experienced in people with Parkinson's disease (PD). It is a predictor of recurrent falls, a barrier to physical exercise, and negatively associated with health-related quality of life. A variety of rating scales exist that assess different aspects of FOF but comprehensive head-to-head comparisons of their psychometric properties in people with PD are lacking. The aim of this study was to evaluate the psychometric properties of four FOF rating scales in people with PD. More specifically, we investigated and compared the scales' data completeness, scaling assumptions, targeting, and reliability. METHODS The FOF rating scales were: the Falls Efficacy Scale-International (FES-I), the Swedish FES (FES(S)), the Activities-specific Balance Confidence scale (ABC), and the modified Survey of Activities and Fear of Falling in the Elderly (mSAFFE). A postal survey was administered to 174 persons with PD. Responders received a second survey after two weeks. RESULTS The mean (SD) age and PD duration of the 102 responders were 73 (8) and 7 (6) years, respectively. ABC had worse data completeness than the other scales (6.9 vs. 0.9-1.3% missing data). All scales had corrected item-total correlations exceeding 0.4 and showed acceptable reliabilities (Cronbach's alpha and Intraclass Correlation Coefficient (ICC) >0.80) but only FES-I had ICC >0.90. The standard error of measurements ranged from 7% (FES-I) to 12% (FES(S)), and the smallest detectable differences ranged from 20% (FES-I) to 33% (FES(S)) of the total score ranges. ABC and FES(S) had substantially more outliers than mSAFFE and FES-I (10 and 15 vs. 3 and 4, respectively) when the two test occasions were compared. CONCLUSIONS When assessing FOF in people with PD, the findings in the present study favoured the choice of FES-I or mSAFFE. However, FES-I was the only scale with ICC >0.90 which has been suggested as a minimum when using a scale for individual comparisons.