Over the past decade, there has been a surge of scientific studies on the digital activity of people, such as making mobile calls, texting, e-mailing and posting on social media.
Because nearly all human behaviour leaves a digital footprint, scientists can use such digital activity as a proxy to track human activity in general, for example to study differences between cultures or communities in sleep patterns, work schedules, and leisure activities, researchers said.
They show that people tend to have their personal rhythm of digital activity - almost like a personal signature.
"Each individual follows their own distinctive and persistent daily rhythm," said Doctoral Candidate Talayeh Aledavood, from Aalto University in Finland.
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These personal rhythms could be detected in multiple datasets, and to a similar extent for e-mail, phone calls, and text messages.
"In almost every case, the individual patterns differ strongly from the average behaviour, for example by increased calling frequency during mornings, mid-days, or evenings," said Aledavood, who performed the research with Jari Saramaki, from Aalto University and Sune Lehmann, from Technical University of Denmark.
The researchers believe that there could also be an effect of physiology, for example caused by the difference between morning and evening persons, or by highly individual patterns of alertness during the daylight hours.
"We see this research as a first step of the way to understanding how activity patterns and chronotype are related to other personal characteristics, such as personality or mobility behaviour," said Lehmann.
Researchers show that these personal digital rhythms persist in time, meaning they are truly characteristic for each individual.