VANCOUVER -- A recent study looking at iPhone's built-in pedometers is a step toward using the tool as a clinical intervention in improving people's health, a University of B.C. researcher said.

Smartphones pose an opportunity for researchers to gather objective data on the public's health and physical activity but before they can be used, the accuracy of the devices need to be tested, lead author Mark Duncan said in an interview Saturday.

"This was very much a first step to make sure that we understand what the data looks like and how well it represents the actual behaviour," he said.

The study involved 33 participants testing the phones in regular living conditions and in a lab.

Comparing users' step count on the iPhone pedometer with an accelerometer worn on their waists in their day-to-day life, the study found the iPhone was underestimating the number of steps by 21.5 per cent or 1,340 steps.

The phones fared better in lab tests where accuracy was within five per cent when users walked at a normal pace. At a slow pace of only 2.5 kilometres an hour, the accuracy of the phones dropped between 7.6 and 9.4 per cent.

Duncan said the discrepancy is likely due to people forgetting to carry their phones at all times.

"If someone goes off to the washroom or to the kitchen and leaves their phone on their desk, obviously it's not going to count those steps," he said.

While the accuracy of the device isn't strong enough to be a primary research tool, Duncan said the information is valuable for the average user interested in improving their health.

"If your goal is the standard 10,000 steps per day and the phone says you've completed that, chances are you've done a bit more which is not a bad thing for your health," he said.

It could also be a tool for physicians to monitor and prescribe more activity to their patients, especially as more Canadians carry smartphones.

"There is quite a lot of research saying physicians want to be able to prescribe more physical activity and help their patients to become more physically active but they lack the time and the tools to do so," he said. "This is potentially one tool that a health care provider could use to both assess physical activity and tell their patients to use it as a tool to increase their physical activity."

He said now that researchers understand the accuracy of the devices, they can begin testing whether it's effective to use smartphone pedometers as a motivational tool to increase a user's physical activity.

Smartphones could also be used to complement other studies by providing an indicator of participants' past level of physical activity. Duncan said a challenge with trials is that some people increase their level of activity because researchers are monitoring them, skewing outcomes, and having that historic data can help flag a change in behaviour.

The study was published last month in the Journal of Sports Sciences.