Formative Evaluation of Consumer-Grade Activity Monitors Worn by Older Adults: Test-Retest Reliability and Criterion Validity of Step Counts.

Test-retest reliability and criterion validity of step counting varied across six consumer-grade activity monitors when worn by older adults with self-reported intact and limited mobility. Walk interruptions increased step count error for all monitors, while self-reported mobility limitation did not affect step count error. The hip-worn Fitbit One was the only monitor that exhibited high test-retest reliability and criterion validity.