Abstract

Objectives
The Korean Dizziness Handicap Inventory (KDHI), which includes 25 patient-reported items, has been used to assess self-reported dizziness in Korean patients with Parkinson's disease (PD). Nevertheless, few studies have examined the KDHI based on item-response theory within this population. The aim of the present study was to assess the feasibility and clinimetric properties of the KDHI instrument using polytomous Rasch measurement analysis.
Methods
The unidimensionality, local independence, scale precision, item difficulty (severity), and response category utility of the KDHI were statistically assessed using WINSTEPS version 4.0.1 (Winsteps Inc.; Chicago, IL, USA) based on the Andrich rating scale model. The utilities of the ordered response categories of the three-point Likert scale were analyzed with reference to the probability curves of the response categories. The separation reliability of the KDHI was assessed based on person separation reliability, which is used to measure the capacity to discriminate among groups of patients with different levels of balance deficits.
Results
Principal component analyses of residuals revealed that the KDHI had unidimensionality. The KHDI had satisfactory PSR and there were no disordered thresholds in the three-point rating scale. However, the KDHI showed several issues for inappropriate scale targeting and misfit items (item 1 and 2) for Rasch model.
Conclusions
The KDHI provide unidimensional measures of imbalance symptoms in patients with PD with adequate separation reliability. There was no statistical evidence of disorder in polytomous rating scales. The Rasch analysis results suggest that the KDHI is a reliable scale for measuring the imbalance symptoms in PD patients, and identified

• Keywords: Parkinson’s disease; Dizziness; Rasch analysis; Item-response theory; Validity; Reliability;