By John Dodge

CHICAGO (CBS) — To determine symptoms of depression, doctors may only need to look no further than a patient’s smart phone.

While people can lie on questionnaires and fake it on Facebook with upbeat status updates, the GPS and usage data on their phones can be a good indicator if somebody is depressed, according to a small Northwestern University study, published this week.

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Scientists found that the more time a user spends on their phone, the higher the chance that they might be depressed. The average daily usage for depressed individuals was about 68 minutes. People with no symptoms averaged about 17 minutes.

Where people use their phones is also a predictor of emotional state, the study found.

Using GPS data from the phones of the study participants, people who spend most of their time at home, or in few locations, are linked to depression, researchers concluded. Having an irregular schedule also can prompt feelings of sadness and hopelessness.

Based on the phone data, Northwestern scientists could identify people with depressive symptoms with 87 percent accuracy.

“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,” said senior author David Mohr, director of the Center for Behavioral Intervention Technologies at Northwestern University Feinberg School of Medicine. “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.”

The research could ultimately lead to monitoring people at risk of depression and enabling health care providers to intervene more quickly.

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The study was published July 15 in the Journal of Medical Internet Research.

The smart phone data was more reliable in detecting depression than answers on a questionnaire, the study’s authors said.

“The data showing depressed people tended not to go many places reflects the loss of motivation seen in depression,” said lead author Sohrob Saeb, a postdoctoral fellow and computer scientist in preventive medicine at Feinberg. “When people are depressed, they tend to withdraw and don’t have the motivation or energy to go out and do things.”

The phone usage data didn’t identify how people were using their phones.

Saeb analyzed the GPS locations and phone usage for 28 individuals–20 women and eight men, with an average age of 29–over two weeks. GPS locations were logged every five minutes.

To determine the relationship between phone usage and geographical location and depression, the subjects took a questionnaire used to measure depression at the beginning of the study.

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Of the participants, 14 did not have any signs of depression and 14 had symptoms ranging from mild to severe depression.