Mobile phones may be able to identify whether an individual is likely suffering from depression, according to a study released Wednesday.

Behaviors linked to depression include spending more at home, using one’s phone at higher than average usage rates and having an erratic schedule, said the study by researchers at Northwestern University and published in the Journal of Medical Internet Research.

Depression affects about 14.8 million U.S. adults, according to data from the Anxiety Disorders Association of America, and health care professionals often fail to identify the symptoms, delaying treatment for months or years, the report said.

“The significance of this is we can detect if a person has depressive symptoms and the severity of those symptoms without asking them any questions,” senior author David Mohr, director of the Center for Behavioral Intervention Technologies at Northwestern University Feinberg School of Medicine, said in a press release.

“We now have an objective measure of behavior related to depression. And we’re detecting it passively. Phones can provide data unobtrusively and with no effort on the part of the user,” Mohr added.

Mobile phones have become ubiquitous and can continuously monitor a person’s physical activity, location and environment, researchers said.

For the report, a mobile phone application called “Purple Robot” was attached to the 28 participants’ phones for two weeks to collect GPS location and phone usage data. Half of the participants suffered from mild to severe depression and the other 14 had no signs of depressive symptoms.

The GPS data could be used to determine whether a person was in a stationary state, including at home or in the office, or in a transition state like walking in the street, the report said. It was also used to determine where participants spent most of their time.

Another factor that researchers looked at within the GPS data was to what extent a person’s movements followed a 24-hour or circadian rhythm. For example, a person who leaves for work and returns around the same time every day has a high level of circadian movement, according to the study.

Low levels of circadian movement are highly correlated with depression, the study showed.

Other features detected by Purple Robot included transition time spent traveling from one place to another, total distance moved, phone use frequency and phone use duration, the report said.

The report found that the average daily phone use duration among participants — whose average age was 28 years old — was 41 minutes, with daily frequency of use averaging 14.2 times. The average daily phone usage for depressed individuals was about 68 minutes, whereas it was about 17 minutes for non-depressed people.

"People are likely, when on their phones, to avoid thinking about things that are troubling, painful feelings or difficult relationships — it’s an avoidance behavior we see in depression,” Mohr said in the press release.

Also, people who had mild to severe symptoms of depression were found to move around less and have a less regular schedule, the report found. It added that their findings were consistent with the patterns of loss of motivation, decreased activity and social withdrawal that characterize depression.

“When people are depressed, they tend to withdraw and don’t have the motivation or energy to go out and do things,” Mohr said in the release.

The data on circadian movement, location variance, home stay, phone-use duration and phone-use frequency were “significantly different between participants with no signs of depression and the rest,” the report said.

By scoring individuals on these six features, researchers said they were able to estimate depression on unseen participants with 87 percent accuracy.

The report cautioned that the study was based on a small number of participants, and that the results must be replicated in a larger study to be confirmed. But the study suggests that phone sensors may offer a new way to monitor at-risk populations without having to ask a patient a lot of questions.

Researchers said future studies would look into whether or not changing those behaviors linked to depression had any effect on their mood.

"We will see if we can reduce symptoms of depression by encouraging people to visit more locations throughout the day, have a more regular routine, spend more time in a variety of places or reduce mobile phone use," Sohrob Saeb, a postdoctoral fellow and computer scientist in preventive medicine at Northwestern, said in the release.