Test–retest reliability and limits of agreement of the Six-Spot Step Test in people with Parkinson’s disease

Abstract

Objective: The aim of this study was to evaluate the within-day and day-to-day agreement and reliability of the Six-Spot Step Test in mild to moderately disabled people with Parkinson’s disease. Design: Cross-sectional cohort study. Setting: Outpatient clinics. Subjects: Forty-four people with Parkinson’s disease. Main measure: The Six-Spot Step Test was completed twice on day 1. Two days later, the Six-Spot Step Test was completed again. The agreement was estimated by Bland–Altman statistics with 95% limits of agreement, and reliability was estimated by the intraclass correlation coefficient. Results: Subjects had a mean (SD) age of 67.8 (6.8) years, a median (range) Hoehn and Yahr score of 2.5 (1–4) and a mean (SD) Six-Spot Step Test score of 8.1 (1.8), 7.6 (1.7) and 7.6 (1.6) seconds on test occasions 1 to 3. An agreement for within-day and day-to-day of ±1.8 (±23.7%) and ±2.2 (±26.7%) seconds was found, respectively. The reliability was 0.81 and 0.76 within-day and day-to-day, respectively. A small learning effect was observed (P < 0.05) between the first and second Six-Spot Step Test, but there was no learning between the second and third occasions. Conclusion: The Six-Spot Step Test has an acceptable within-day and day-to-day agreement and reliability in mild to moderately disabled people with Parkinson’s disease. A change of 2.2 seconds can be regarded as a true change. To minimize learning effects, test trials of the Six-Spot Step Test are recommended before use.