Concurrent Criterion Validity of a Test of Usual Gait Speed in Older Adults.

Usual gait speed has been shown to have very good reliability and convincing predictive validity for evaluating older adults' gait skills, but its criterion validity is unknown. We examined the criterion validity of the 8-feet (i.e., 2.44 meters) test in a laboratory environment to assess usual gait speed by comparing its results with the Intelligent Device for Energy Expenditure and Activity (IDEEA) monitor. Participants were 200 well-functioning community-dwelling adults aged 65 and older (113 women; 87 men; mean [M] age = 71.8, standard deviation [ SD] = 5.6 years). Participants wore the IDEEA monitor for 48 consecutive hours, and we used the participants' average usual gait speed for the analysis. The Spearman correlation of usual gait speed using both the 8-feet test and IDEEA monitor was moderate and statistically significant (ρ = .364, p < .001). The mean difference between both methods was 0.20 ( SD = 0.27) meters/second, and the corresponding limits of agreement were 0.73 and -0.33 meters/second. There was a small systematic bias when the difference between the two methods was correlated with usual gait speed as measured by the IDEEA (ρ = -.20, p = .011). The perfect agreement (weighted kappa) of both instruments for classifying usual gait speed into tertiles, quartiles, and quintiles was 48.3% ( k = 0.17), 30.9% ( k = 0.23), and 25.4% ( k = 0.29), respectively. Our results indicate that the 8-feet test showed moderate criterion-related validity for evaluating and assessing usual gait speed test in older adults.