This study will determine whether the Medibio Depression Diagnostic Aid exceeds minimally acceptable thresholds for sensitivity and sensitivity in cases with a current depression episode and non-depressed controls.

Subjects meeting study criteria will be enrolled into one of two study cohorts: a) outpatient individuals with current, moderate-to-severe major depressive episode (experimental group) and b) individuals without current major depressive episode that have been matched at the group level for age and gender (control group).

All subjects will undergo two separate psychiatric interviews to confirm current depression episode presence or absence. Thereafter subjects will wear a heart rate monitor on the chest to capture data over the course of 72 hours. Subjects will return approximately 1 week after initial placement of the monitor for equipment return and a safety check. Subjects will wear a heart-rate monitor over the course of 72 hours. Subjects will return within a week from the last visit for equipment return.

All Subjects:

Inclusion Criteria:

• Subject is willing and able to provide consent.
• Subject has ability to read and understand the instructions for the study.
• Subject is willing to adhere to study procedures.

Exclusion Criteria:

• Subject has active psychotic symptoms.
• Subject has bipolar disorder.
• Subject has known, or is suspected to have a personality disorder.
• Subject has current suicidality of medium or high risk as determined by M.I.N.I. or HAMD-17 item #3 score of 3 of higher.
• Subject has history of central or obstructive sleep apnea OR STOP-BANG questionnaire score of ≥5.
• Subject has a pacemaker.
• Subject currently uses benzodiazepines on a scheduled basis.
• Subject currently uses chronotropic medication, such as beta-blockers, digoxin, sinoatrial/atrioventricular nodal-acting calcium channel blockers, or amiodarone.
• Subject is suspected or known to have active alcohol or drug abuse (including but not limited to abuse of marijuana).
• Subject has a terminal illness.
• For female subjects, subject is currently known to be pregnant or lactating.
• Subject has any other acute or chronic condition that in the investigators opinion would preclude the subject from being able to meet all of the protocol requirements, or would compromise the subject's safety during participation in the study, as judged by the investigator.
• Subject is currently participating in another clinical study. Subject currently uses antipsychotic medication for any indication.

Depressed Cohort Inclusion Criteria: Subject has current moderate or severe Major Depressive Disorder Episode, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I plus HAMD-17 rating scale score ≥17.

Exclusion Criteria: Subject has presence of no or mild Major Depressive Disorder Episode, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I OR HAMD-17 rating scale score <17.

Control Cohort Inclusion Criteria: Subject has no presence of mild, moderate, or severe Major Depressive Disorder Episode, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I AND HAMD-17 rating scale score ≤7.

Exclusion Criteria: Subject has presence of mild, moderate, or severe Major Depressive Disorder Episode, based on DSM-IV criteria for diagnosis as documented by clinician administered M.I.N.I OR HAMD-17 rating scale score >7.

Subjects who may be currently experiencing an episode of depression that are being diagnosed or treated in a mental health setting.

IPD will not be shared with other researchers.