Abstract: An automated system may estimate a patient's level of depression throughout a monitoring period. The system may do so without ever receiving any self-reports from the patient, such as patient answers to a survey regarding the patient's affect. The system may predict the patient's depression level based on passive sensor data regarding the patient during the monitoring period. The passive sensor data may include physiological measurements, such as electrodermal activity measurements and accelerometer measurements. The passive data may also comprise data regarding the patient's smartphone and texting usage. The system's predictions may also be based on a single depression rating for the patient by a clinician, without any further assessments by the clinician.