Thirty second chair stand test: Test-retest reliability, agreement and minimum detectable change in people with early-stage knee osteoarthritis

Background and Purpose: To determine intra-session test-retest reliability, agreement and minimum detectable change (MDC) of the 30 CST across three tests in people with knee osteoarthritis (OA). Methods: A test-retest reliability study was performed with 93 people with mild radiological knee OA. Participants were asked to complete three attempts of the 30 CST 1-2 min apart according to a standardised protocol. Participants completed three attempts on two occasions: baseline and 6 months later. Change between tests within each session was assessed with ANOVA's and post-hoc t-tests. Reliability was assessed with intra-class correlation coefficients (ICC[2,(1])). Measurement error was expressed as MDC for an individual (MDCind) and a group (MDCgroup). Floor effects were considered present if more than 15% of participants scored zero for a test. Results: Scores increased by 0.5 and 0.8 stands between the first and second test (p < 0.05) at the baseline and 6-month assessments respectively, and then stabilised between the second the third tests at the baseline assessment (p > 0.05) or decreased (0.3 stands) at the 6-month assessment (p < 0.05). Scores demonstrated excellent reliability (ICCs >0.9). MDCind was approximately 2.5 stands and MDCgroup was 0.3-0.4 stands. No floor effects were apparent. Discussion: The 30CST demonstrated a practice effect between the first and second tests, which was no longer apparent by the third test. Despite this, scores demonstrated excellent intra-session reliability. MDC estimates provide clinicians and researchers with the smallest change that can be detected by the instrument beyond measurement error for individuals and groups in community-dwelling adults with knee OA.