The relative and absolute reliability of the Functional Independence and Difficulty Scale in community-dwelling frail elderly Japanese people using long-term care insurance services

Background The newly developed Functional Independence and Difficulty Scale is a tool for assessing the performance of basic activities of daily living in terms of both independence and difficulty. The reliability of this new scale has not been assessed. Aims The aim of this study was to examine the relative reliability and absolute reliability of the newly developed scale in community-dwelling frail elderly people in Japan. Methods Participants were 47 community-dwelling elderly subjects (22 for assessing test–retest reliability and 25 for assessing inter-rater reliability). As relative reliability indices, intra-class correlation coefficients were used. From an absolute reliability perspective, we conducted Bland–Altman analysis and calculated the limit of agreement or minimal detectable change to determine the acceptable range of error. Results Intra-class correlation coefficients for test–retest and inter-rater reliability were 0.90 ( P