Measurement properties of the Falls Efficacy Scale-International (FES-I) in persons with late effects of polio: A cross-sectional study

Background Fear of falling (FoF) is very common in persons with late effects of polio (LEoP). An internationally recognized rating scale to assess FoF is the Falls Efficacy Scale-International (FES-I). Yet, there is limited knowledge about its measurement properties in persons with LEoP. Objective To investigate the measurement properties of the FES-I (16-item version) and the short FES-I (7-item version) in persons with LEoP. Design Explorative factor analysis and Rasch model analysis of cross-sectional data. Setting University hospital. Participants A total of 321 persons with LEoP (mean age +/- standard deviation [SD] 70 +/- 10 years, 173 women). Main Outcome Measurement The FES-I and the short FES-I, comprising four response options about concerns of falling ranging from 1 (not at all concerned) to 4 (very concerned). Methods Data were collected by a postal survey. First, a factor analysis was performed to investigate the unidimensionality of the scale. Thereafter, a Rasch model analysis was used to further analyze the measurement properties of the FES-I and the short FES-I, such as local dependency, targeting, hierarchical order of items, Differential Item Functioning (DIF), response category functioning and reliability (Person Separation Index, PSI). Raw score transformation to interval measurements was also performed. Results The factor analysis revealed that the FES-I was unidimensional, even though the Rasch analysis showed some misfit to the Rasch model and local dependency. Targeting for the FES-I and the short FES-I was somewhat suboptimal as the participants on average reported less FoF than expected. A negligible gender DIF was found for two items in the FES-I and for one item in the short FES-I. Reliability was high (PSI >0.86), and the response category thresholds worked as intended for both the FES-I and the short FES-I. Conclusion The FES-I and the short FES-I have sufficient measurement properties in persons with LEoP. Both versions can be used to assess fear of falling (or FoF) in this population.