Validity, reliability, and measurement error of the Japanese version of the Freezing of Gait Questionnaire for patients with Parkinson's disease.

Background: The Freezing of Gait Questionnaire has been translated into several languages. However, it has not been translated into Japanese and its measurement error remains unclear. Objectives: This study aimed to translate the Freezing of Gait Questionnaire into Japanese, investigate its validity and reliability, and calculate its measurement errors.
Methods: Thirty-five patients with Parkinson's disease participated in the study. The Freezing of Gait Questionnaire was translated into Japanese using a forward - backward translation method. Convergent validity was assessed using the Freezing of Gait Questionnaire and Unified Parkinson's Disease Rating Scale Part II(item 14-freezing). The content validity index was calculated using the Freezing of Gait Questionnaire score using correlation coefficients. Internal consistency was measured using Cronbach's alpha. The test - retest reliability was evaluated using the intraclass correlation coefficient(1,1). The Bland - Altman analysis was performed to detect the limits of agreement.
Results: The mean Freezing of Gait Questionnaire score was 9.1 (5.0) points. Convergent validity was 0.655 and content validity index was 0.958. Cronbach's alpha was 0.958, intraclass correlation coefficient(1,1) was 0.951, and the limits of agreement ranged from - 4.9 to3.2 points.
Conclusions: The Japanese version of the Freezing of Gait Questionnaire is a valid and useful tool to evaluate patients with Parkinson's disease.