Reliability and measurement error of the Osteoarthritis Research Society International recommended performance-based tests of physical function in people with hip and knee osteoarthritis

Summary Objective To estimate the reliability and measurement error of performance-based tests of physical function recommended by the Osteoarthritis Research Society International in people with hip and/or knee osteoarthritis. Design Prospective repeated measures between independent raters within a session and within-rater over a week interval. Relative reliability was estimated for 51 people with hip and/or knee osteoarthritis (mean age 64.5 years, SD 6.21 years; 47% females; 36 (70%) primary knee OA) on the 30s Chair Stand Test (30sCST), 40m Fast Paced Walk Test (40mFPWT), 11-Stair Climb Test (11-step SCT), Timed Up and Go (TUG), Six Minute Walk Test (6MWT), 10m Fast Paced Walk Test (10mFPWT) and 20s Stair Climb Test (20sSCT) using intra-class correlation coefficients (ICC). Absolute reliability was calculated using standard error of measurement (SEM) and minimal detectable change (MDC). Results Measurement error was acceptable (SEM 0.9, lower 1-sided 95% CI > 0.7) for the 40mFPWT, 6MWT and 10mFPWT; sufficient (ICC >0.8, lower 1-sided 95% CI >0.7) for 30sCST, 20sSCT; unacceptable (lower 1-side 95%CI