A study of the inter-rater reliability of a test battery for use in patients after total hip replacement

Objective: To assess the within-day inter-rater reliability of a test battery of functional performance, muscle strength and leg extension power on total hip replacement patients. Design: A test-retest design was used. Setting: Orthopaedic department at a Regional Hospital in Denmark. Subjects: Two convenience samples of 20 total hip replacement patients were included. Intervention: The tests were performed three months after total hip replacement. Two raters performed test and re-test, with two hours rest in-between. Main measures: The test battery included: sit-to-stand performance, 20-metre maximum walking speed, stair climb performance, isometric muscle strength (hip abduction/flexion), and leg extension power. Absolute reliability was assessed with Bland Altman plots, standard error of measurement (SEM), and minimal detectable change. Relative reliability was assessed with intra-class correlation coefficient. Results: Systematic differences between testers were seen in tests of walking speed (0.32 seconds p = 0.03) and stair climb performance (0.18 seconds p = 0.003). In per cent of the grand mean, the standard error of measurement was 3%-10%, indicating the measurement error on a group level, and the minimal detectable change was 10%-27%, indicating the measurement error on an individual level. The intra-class correlation coefficients were above 0.80 in all tests (range 0.83-0.95). Conclusions: The tests showed acceptable relative and absolute inter-rater reliability on a group level, but not on an individual level (except from test of walking speed and stair climb performance). Systematic differences between testers were considered clinically irrelevant (0.3 and 0.2 seconds).