In 2017, depression became recognised as the leading cause of ill health and disability worldwide.1 In England, 1 in 6 people experience mental health problems every week,2 75%3 of whom may not be able to access the treatment they need. There is a growing interest in electroencephalogram (EEG) analysis to identify anomalous patterns of electrical activity in the brains of depressed patients. These patterns are known as EEG phenotypes.