Activity tracking apps on smartphones are more accurate than fitness tracking wearables when it comes to step counts, according to a small study conducted by researchers at the University of Pennsylvania. Interestingly, the study found that clip-on pedometers were the most accurate.

“Since step counts are such an important part of how these devices and apps measure physical activity, including calculating distance or calories burned, their accuracy is key,” senior author and assistant professor at the University of Pennsylvania, Mitesh Patel, said in a statement. “Compared to the one to two percent of adults in the US that own a wearable device, more than 65 percent of adults carry a smartphone. Our findings suggest that smartphone apps could prove to be a more widely accessible and affordable way of tracking health behaviors.”

The researchers recruited 14 users who wore one pedometer and two accelerometers on their waistband, three wearable devices on their wrist, and two different smartphones in their pockets -- one running three apps and the other running one -- during the study. 

One of the smartphones used, the iPhone 5S, ran apps from Fitbit, Withings, and Moves. The other phone, Galaxy S4 ran the Moves app. The three wearable devices were Nike FuelBand, Jawbone UP24, and Fitbit Flex. Finally, the pedometers used were Fitbit One, Fitbit Zip, and Digi-Walker SW-200.

Each participant walked on a treadmill set at three miles per hour for 500 steps and 1,500 steps two times. An observer counted the steps using a tally counter.

Researchers found that the relative difference in mean step count ranged from -0.3 percent to 1 percent for pedometers, -6.7 percent to 6.2 percent for the apps, and -22.7 percent to -1.5 percent for wearable devices. The Nike FuelBand was the least accurate wearable tracker -- the device reported step counts more than 20 percent lower than observed.

This study was funded, in part, through a grant from the National Institute on Aging.