Reliability of digitally instructed self-reported 30-second chair stand test for lower extremity function.

Objective: The 30-s Chair Stand Test (30s CST), a valid and reliable test evaluating lower extremity physical function, has been integrated into a digital eHealth program. We aimed to evaluate the agreement (inter-rater reliability) between digital self-assessment and in-person physiotherapist assessment as well as intra-rater test-retest reliability of digital self-assessment among persons with hip or knee osteoarthritis. Design: Eligible participants with hip or knee osteoarthritis were identified from the digital treatment database. The 30s CST was performed through a digital self-assessment and in-person physiotherapist assessment. The inter-rater reliability study was conducted at a physiotherapy clinic and for the intra-rater test-retest reliability, the participants performed the digitally self-assessment test twice in their home. Results: The inter-rater reliability one-day study, included 18 participants (mean age 67 years and 89 ​% females) and one physiotherapist. The intra-rater test-retest, separated by 10-14 days, included 54 participants (mean age 69 years, 78 ​% females). There were, on average, 1.5 (95 ​% CI 0.6 to 2.4) more self-reported sit-to-stand repetitions for the digital self-assessment compared with in-person physiotherapist assessment. The digital self-assessment of 30s CST showed low to excellent inter-rater reliability with an intraclass correlation coefficient (ICC) of 0.87 (95 ​% CI 0.47 to 0.96) and good to excellent intra-rater test-retest reliability, ICC 0.88 (95 ​% CI 0.79 to 0.93). Bland-Altman plots suggested good levels of inter- and intra-rater reliability. Conclusion: Results suggest that the 30s CST can be measured digitally as a self-administered and self-reported measurement of lower extremity physical function in older adults with hip and/or knee osteoarthritis.