The reliability, and discriminative ability of the identification of functional ankle instability questionnaire, Japanese version.

Objective: To assess the discriminability as well as the reliability, and internal consistency of the Identification of Functional Ankle Instability questionnaire translated into Japanese (IdFAI-J).

Design: Cross-sectional study.

Setting: Collegiate athletic training/sports medicine clinic.

Participants: Twenty bilingual and sixty-five collegiate athletes including participants with and without functional instability (FI).

Main Outcome Measures: The sensitivity, specificity, test retest reliability, and internal consistency of IdFAI-J.

Results: The optimal cutoff score between the FI and non-FI participants was >10, with an area under the curve of 0.92. We calculated high sensitivity (0.94) and specificity (0.77) at the cutoff point. For the test-retest reliability, the intraclass correlation coefficient value of the IdFAI-J was 0.96; the standard error of measurement and minimal detectable change value was 1.69 and 3.60, respectively. Cronbach's α was 0.87; there was no improvement when a particular item was deleted from the scale.

Conclusions: The IdFAI-J has excellent discriminability, test-retest reliability, and internal consistency. Hence, the IdFAI-J significantly contribute to clinical practice and future research related to ankle instability in Japan.