Smartphones could help determine when their users are depressed. In a recent study, researchers tested an app called Purple Robot to detect depression from an individual's smartphone sensor data.

The researchers at Northwestern University tracked the number of minutes for which the phone was used by the users and their daily geographical locations. The results were exciting as depression was precisely detected, and are researchers claiming that people with depressive symptoms can be successfully identified by the app with 87% accuracy.

Sohrob Saeb, one of the developers of Purple Robot, said the app was developed with the sole aim of objectively and passively identifying people with depression.

The study saw tracking of 40 people between the ages of 19 and 58 for two weeks. The researchers found that numbers of minutes spent on using phone were linked to depression. The more the time used on phone, the more the chances of depression.

The researchers said 68 minutes was the average daily usage for depressed individuals, while 17 minutes was for non-depressed individuals.

"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. We now have an objective measure of behavior related to depression. And we're detecting it passively", said David Mohr, senior author of the study.

The researchers also found that depression comes from spending most of the time at home and most of the time in fewer locations. A less regular day-to-day schedule is also linked to depression.