Digital Phenotypes for Predicting Depression

This is a 12-month longitudinal follow-up study designed to identify digital phenotypes capable of predicting the recurrence of major depressive episodes using passively collected real-time data from smartphones and wearable devices. A total of 540 participants will be enrolled, including 200 patients diagnosed with mood disorders who have experienced at least one depressive episode in the past two years, and 340 healthy or high-risk control participants without a clinical diagnosis.

Clinical interviews and self-report measures will be conducted five times at 3-month intervals. Throughout the study period, participants will wear a Fitbit device daily and use the "My Mental Hero" mobile application to record their mood once a day at a self-selected time. Data collected will be used to develop machine learning models for predicting depressive recurrence and to build a large-scale, anonymized wearable big-data repository for mood disorders.

Participants will receive no interventions beyond data collection, and neither randomization nor blinding will be implemented. Trained psychiatrists, clinical psychologists, or research nurses will conduct the assessments. Initial visits will include informed consent, device setup, and app training, taking approximately 1-2 hours. Subsequent assessments will take about one hour, with additional brief interviews (≤30 minutes) conducted if a mood episode is suspected.

While follow-up assessments for patients and high-risk participants will be conducted in person, those for healthy controls may be conducted remotely (via Zoom or phone) under secure and private conditions without screen recording. Remote assessments may also be used for patient and high-risk groups if necessary.

Inclusion criteria

for Patient Group:

• Adults aged 19 to 75 years and 11 months.
• Diagnosed with a major mood disorder (bipolar I or II disorder, or major depressive disorder) based on DSM-5, with a history of psychiatric visits for mood symptoms.
• Has experienced at least one prior depressive episode (major, minor, or brief).
• Owns a smartphone with stable internet connectivity, can operate it without difficulty, and agrees to install a digital phenotyping application, wear a Fitbit device daily, and complete daily mood logs throughout the study period.

Inclusion criteria

for Healthy Control Group:

• Adults aged 19 to 75 years and 11 months.
• No current or past diagnosis of bipolar disorder or major depressive disorder.
• Scores below clinical thresholds on both K-MDQ (<7) and PHQ-9 (<5) at baseline assessment.
• Owns a smartphone with stable internet connectivity, can operate it without difficulty, and agrees to install a digital phenotyping application, wear a Fitbit device daily, and complete daily mood logs throughout the study period.

Inclusion criteria

for Hight Risk Group:

• Adults aged 19 to 75 years and 11 months.
• No current or past diagnosis of bipolar disorder or major depressive disorder.
• Meets either of the following:

A. Scores above the threshold on K-MDQ (≥7) or PHQ-9 (≥5) at baseline. B. Reports persistent mood symptoms during MINI (e.g., ≥2 weeks of depressive mood/anhedonia, or several days of elevated/irritable mood).

• Owns a smartphone with stable internet connectivity, can operate it without difficulty, and agrees to install a digital phenotyping application, wear a Fitbit device daily, and complete daily mood logs throughout the study period.

Exclusion Critera (Overall)

• Inability to provide informed consent due to cognitive impairment, severe psychiatric symptoms, or language barriers.
• Presence of any neurological or medical condition that may significantly affect mood, cognition, or behavior (e.g., epilepsy, dementia, traumatic brain injury).
• Current substance use disorder or dependence (excluding nicotine or caffeine) that is either untreated or clinically unstable.
• Severe suicidal ideation or risk as determined by clinical judgment at screening.
• Ongoing participation in another interventional clinical trial, particularly those involving psychotropic medications or digital health interventions.
• Inability or unwillingness to wear a wearable device (Fitbit) or use the required mobile application daily throughout the study.
• Lack of stable internet access or a compatible smartphone required for digital phenotyping data collection.
• Any other condition that, in the investigator's judgment, may compromise the participant's safety, compliance, or the integrity of the study data.