Test-retest reliability, internal consistency, and discriminant validity of the Filipino version of Knee injury and Osteoarthritis Outcome Score among community-dwellers with knee osteoarthritis

Objective: This study aimed to determine the test-retest reliability, internal consistency, and discriminant validity of the Filipino Knee injury and Osteoarthritis Outcome Score (F-KOOS) among community-dwellers with knee osteoarthritis (OA). The study also examined the suitability of the F-KOOS in terms of relevance and ease of understanding. Methods: This psychometric study utilized a cross-sectional design. Participants (>50 years old) with knee pain and soreness were recruited from the community and were medically diagnosed with knee OA according to the American College of Rheumatology clinical criteria. Participants were instructed to report for two sessions approximately two weeks apart. Descriptive statistics were used to describe the characteristics of participants and suitability in answering F-KOOS. Test-retest reliability and internal consistency were determined through intraclass correlation coefficients (ICCs) and Cronbach alpha, respectively. Discriminant validity was examined by comparing those with and without knee OA using independent t-test (p<0.05) per F-KOOS subscale. Results and Discussion: A total of 53 participants (35 females, 18 males) with a mean age of 69.67+5.83 years old were included in the study. The domains of the KOOS in the pre-test and re-test range from 0.30 to 0.78 (p<0.05), indicating good test-retest reliability between two assessment points. All domains of the F-KOOS had high internal consistency (Cronbach alpha of > 0.7) ranging from 0.87 to 0.96. Discriminant validity of all domains of F-KOOS between participants diagnosed with and without knee OA showed p-values <0.01 which indicate a significant difference between both groups. In terms of preference, out of 40 participants who answered the survey, 55-85% expressed ease and satisfaction in answering F-KOOS. Conclusion: The study demonstrated that the F-KOOS has an acceptable test-retest reliability, good internal consistency, and discriminant validity in individuals with knee OA. The study further determined that the use of the F-KOOS is appropriate, relevant, and easy to understand in the community setting.