Test--retest reliability of the StepWatch Activity Monitor outputs in individuals with chronic stroke.

OBJECTIVE To examine the test-retest reliability of the StepWatch Activity Monitor outputs over two periods, a week apart, in participants with stroke. DESIGN Test-retest reliability study over monitoring periods of one, two and three days. SETTING Participant's usual environment. PARTICIPANTS Forty participants more than six months post stroke. MAIN MEASURES StepWatch outputs: total step count, number of steps at high medium and low stepping rates, sustained activity indices, peak activity index. RESULTS The intraclass correlation coefficients were high for all StepWatch outputs and all monitoring periods but were highest for the three-day monitoring period (0.930-0.989) and lowest for the one-day monitoring period (0.830-0.950). The coefficient of variation ranged from 6.7% to 48.7% over the monitoring periods, with higher variation shown for shorter monitoring periods. The most reliable four outputs had 95% limits of agreement between three-day periods that were less than 40%. These were total step count (+/-37.8%), highest step rate in 1 minute (+/-23.0%), highest step rate in 5 minutes (+/-38.6%) and peak activity index (+/-29.8%). The highest step rate in 1 minute was the only StepWatch output that had 95% limits of agreement less than 40% for the two-day (+/-31.2%) and one-day (+/-36.7%) monitoring periods. CONCLUSIONS Total step count, highest step rate in 1 minute, highest step rate in 5 minutes and peak activity index have good test-retest reliability over a three-day monitoring period, with lower reliability shown by the other StepWatch outputs. In general, monitoring over one or two days is less reliable.