The Cumberland ankle instability tool: a report of validity and reliability testing.

Objective: To test the Cumberland Ankle Instability Tool (CAIT), a 9-item 30-point scale, for measuring severity of functional ankle instability.
Design: Cross-sectional study.
Setting: General community.
Participants: Volunteer sample of 236 subjects.
Interventions: Not applicable.
Main Outcome Measures: Concurrent validity by comparison with the Lower Extremity Functional Scale (LEFS) and a visual analog scale (VAS) of global perception of ankle instability by using the Spearman rho. Construct validity and internal reliability with Rasch analysis using goodness-of-fit statistics for items and subjects, separation of subjects, correlation of items to the total scale, and a Cronbach alpha equivalent. Discrimination score for functional ankle instability by maximizing the Youden index and tested for sensitivity and specificity. Test-retest reliability by intraclass correlation coefficient, model 2,1 (ICC(2,1)).
Results: There were significant correlations between the CAIT and LEFS (rho=.50, P<.01) and VAS (rho=.76, P<.01). Construct validity and internal reliability were acceptable (alpha=.83; point measure correlation for all items, >0.5; item reliability index, .99). The threshold CAIT score was 27.5 (Youden index, 68.1); sensitivity was 82.9% and specificity was 74.7%. Test-retest reliability was excellent (ICC(2,1)=.96).
Conclusions: CAIT is a simple, valid, and reliable tool to measure severity of functional ankle instability.