Schematic showing one aspect of how smartphone-based digital phenotyping may be used to learn about a subject’s phone-mediated communication patterns and how those patterns might change over time in a hypothetical patient. The study subject is shown in blue in the top panel and the arrows between the subject and his social contacts represent communication flows over a period of time. Anonymized phone call logs (bottom panel) capture the underlying communication events, where each horizontal bar represents incoming and outgoing calls between the subject and one of his contacts. These data can be used to investigate call reciprocity (middle panel), a measure reflecting the balance between incoming and outgoing communication flows. A depressed subject might have reduced likelihood of returning calls, leading to low call reciprocity, but, as the patient improves, his call reciprocity might be expected to return to typical levels (blue band).