6th vital sign app: Testing validity and reliability for measuring gait speed

Gait speed tests are useful predictors of different health outcomes in people. These tests can be administered by the convenience of one's smartphone.

Is the 6th Vital Sign app valid and reliable for measuring gait speed?

The study used a prospective test-retest design. Fifteen college subjects were asked to walk at their normal pace for 2 min. Each subject performed two trials. Speed was recorded by the 6th Vital Sign app, Brower timing gates, and by hand-measurement of distance walked divided by the 2 min. Criterion validity was assessed by paired t-tests, Cohen's D effect sizes, and Pearson correlation tests. Inter-trial reliability within each device was assessed with Pearson correlation tests.

Speed measured by the app was significantly lower than speed measured by gates (p = 0.004) and by hand-measurement (p = 0.009). The difference between gates and hand-measurement was not significant (p = 0.684). The speed measured by gates and hand-measurement were very highly correlated (r = 0.974), but speed measured by app was only moderately correlated with gates (r = 0.370) and hand-measurement (r = 0.365). The inter-trial reliability was fairly high with correlations r = 0.916, 0.944, and 0.941 when speed was measured by the app, gates, and hand-measurement, respectively.

The app tended to underestimate speed when compared to gate and hand-measurements. Therefore, we conclude that the 6^th Vital Sign app is not valid for use for clinical diagnosis or prognosis.