Mental health

Weak link between depression and frequent smartphone use

"Smartphone behaviour 'could diagnose depression' says new scientific study," the Daily Mirror reports. But based on the data presented in the study the paper is reporting on, we would disagree.

The story was prompted by a small US study of adults who agreed to have a freeware app – Purple Robot – installed on their phone. The app tracks phone usage and physical movement via GPS.

Researchers found people who reported depressive symptoms used their phone more often, visited fewer locations, and spent more time at home than the group of people who did not have symptoms of depression.

The results should not be taken too seriously as these two groups of people were not matched, so other factors could have influenced the results (confounders).

A major factor that was not accounted for was whether any of the people involved in the study were employed, the nature of the employment, or whether they were looking after children or caring for someone. This would have had a major impact on their phone use and the amount of time they spent going out to different places.

Other factors commonly taken into account but not included in this study are a history of mental health problems, age, sex and any medical or psychiatric conditions.

In short, this study does not show smartphone use can diagnose depression.  

Where did the story come from?

The study was carried out by researchers from Northwestern University and Michigan State University, and was funded by the US National Institute of Mental Health.

It was published in the peer-reviewed Journal of Medical Internet Research.

The authors do not declare any conflict of interest. They developed an open-source app called Purple Robot, which is designed to collect mobile phone sensor data.

Purple Robot has also been used in studies designed to optimise adherence to treatment regimes for people with HIV, ulcerative colitis and Crohn's disease.

The Mail Online coverage of the story included some inaccuracies, such as saying, "The phone data turned out to be a more reliable way of detecting depression than asking participants questions about how sad they were feeling on a scale of one to 10".

But the scales used were from one to three, and it is not clear how the phone data could be "more reliable" when none of the participants were assessed for symptoms of depression other than their answers to this symptom-scale questionnaire.

The Mail also says that, "Using a phone stops people dealing with difficult feelings" without pointing out this was just the authors' hypothesis and not actually assessed in the study.

Similarly, the Daily Mirror carried a number of quotes from the lead author, such as, "We now have an objective measure of behaviour related to depression", without subjecting these comments to any scrutiny.  

What kind of research was this?

This observational study aimed to see if people who self-reported symptoms of depression were likely to use their mobile phones more than people who did not have symptoms of depression.

It also aimed to see if they were less likely to go out to different places.

This type of study can only show an association and cannot prove cause and effect.

What did the research involve?

Forty adults aged between 19 and 58 were recruited to take part in the study. They were asked to download an app called Purple Robot on to their phone.

This app measured their phone usage and mapped their location using GPS. The participants were asked to keep the phone with them at all times for two weeks.

At the beginning of the study they completed the Patient Health Questionnaire-9 (PHQ-9) to record any self-reported symptoms of depression. This questionnaire asks people to rate nine different symptoms of depression from 0 (not at all) to three (nearly every day). Scores can range from 0 to 27.

This screening questionnaire gives an indication of whether a person is likely to be depressed, but a diagnosis would require further clinical assessment. The scores suggest the following:

  • 5 to 9 – mild depression
  • 10 to 14 – moderate depression
  • 15 to 19 – moderately severe depression
  • 20 or more – severe depression

The researchers split the people into two groups – one group scored less than five on the PHQ-9 and the other group scored five or more. The researchers then analysed the results looking for any associations between depressive symptoms, phone usage and how much a person was out and about.  

What were the basic results?

Data was available for only 28 of the participants, with 14 in each group. The average PHQ-9 score for the depressive group was 9.6, which would be rated as mild.

People with depressive symptoms went out less often and spent more time at home. They also used their phone more often, but the study doesn't report if these participants used their phone for texting, surfing the internet or talking to someone.  

How did the researchers interpret the results?

The researchers concluded mobile phone use could be used to help identify people with depressive symptoms.

They say that, "While these findings must be replicated in a larger study among participants with confirmed clinical symptoms, they suggest that phone sensors offer numerous clinical opportunities, including continuous monitoring of at-risk populations with little patient burden and interventions that can provide just-in-time outreach." 


This small study suggests people who report higher levels of depressive symptoms may use their phone more and go out less.

However, these findings should not be taken too seriously as this study has many limitations, including:

  • a small sample size – data from only nine people in each group was used for the location data
  • there was no attempt to ensure the two groups were matched in terms of any medical illness, age, sex, whether they were employed, or any other potential confounding factors
  • it's not known whether any of the participants in either group had a diagnosis of depression or any other mental illness
  • the analysis relied on the participants keeping their mobile phone with them continuously, which may or may not have actually happened

In short, this study does not show that mobile phone use can diagnose depression. As the researchers point out, a much larger – and, in our opinion, better designed – study would be required to see if a depression app or similar would be a viable idea.

If you are feeling low, it is a good idea to talk to someone or seek professional help. The Samaritans are available 24 hours a day, 365 days a year if you are in distress and can be reached on 08457 90 90 90.

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