How your cellphone knows if you’re depressed. It has to do with how you move through time and space.

A growing number of scientists are starting to mine cellphone data in the hopes that it will help them understand what makes you happy or sad, and pinpoint signs of a disease long before it can be diagnosed by a blood sample or MRI, helping you live longer and better. In one of the first of a number of studies in the works to be published, researchers at Northwestern University Feinberg School of Medicine believe they have found a way for your smartphone to determine if you're depressed. In a study published July 15 in the Journal of Medical Research, they report that the more time you spend using your phone the more likely it is that you're depressed. That link didn't hold true for 100 percent of people, however. A second analysis that looked at how people move through time and space showed stronger correlations. By using this data the researchers were able to identify people with depressive symptoms with a startling 87 percent accuracy although they noted that the results are based on a small sample size and are therefore preliminary.

The implications of this type of work are enormous, not only for the future of health care but for people's privacy. It wasn't so long ago that people worried about the data collected by marketers using information about your purchasing habits from your credit card, marketing surveys and zipcode. That amount of information seems very limited now in comparison to the intimate moments and habits your cellphone is logging every second.