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Social media privacy is in the hands of a few friends

January 21, 2019

New research has revealed that people's behaviour is predictable from the social media data of as few as eight or nine of their friends.

Published today in the journal Nature Human Behaviour, a study from the University of Adelaide in Australia and the University of Vermont in the US has found that even where people have deleted their accounts they can be profiled from the information that can be drawn from their friends' posts.

This is the first study to determine the extent to which information about individuals is encoded in their interactions with friends.

"Effectively it shows that there is no place to hide on social network platforms," says co-author Dr Lewis Mitchell, Senior Lecturer in applied mathematics in the University of Adelaide's School of Mathematical Sciences and Associate Investigator with the ARC Centre of Excellence in Mathematical and Statistical Frontiers (ACEMS).

"Telling people to delete your account in order to protect your privacy is not enough, as profiling information such as someone's political affiliations or leisure interests can be determined from your friends' posts.

"It's like listening in on one end of a phone call. Even though you can't hear the person on the other end of the line, you can still find out a lot of information about them from the one-sided conversation you can hear."

The researchers analysed the information content of over 30 million Twitter messages using information theory from mathematics and probability to test the predictability of individuals' behaviour, based on the text they publish online.

They showed that up to 95% of the potential accuracy for an individual is achievable using data from their friends alone. And data from 8-9 friends was enough to obtain predictability comparable to that using only the individual's data.

"Many people know they are giving out access to their information when choosing to use an online platform, but they think it's only information about themselves," says co-author Dr James Bagrow, Assistant Professor, Mathematics and Statistics and Vermont Complex Systems Center at the University of Vermont. "But it's not an individual choice: they're also giving away information about their friends."

Dr Mitchell adds: "There are benefits from being able to predict behaviour. Social media platforms use this principle to target information so that you receive posts that you are interested in.

"But of course there is a dark side as well, such as the potential for the creation of 'filter bubbles'. For instance in a political debate, people may be only exposed to one type of information and may not receive any opposing views," Dr Mitchell says.
Media Contact:

Dr Lewis Mitchell, Senior Lecturer in Applied Mathematics, School of Mathematical Sciences, University of Adelaide. Phone: +61 8 8313 5424. Mobile: +61 (0)478 146 773,

Robyn Mills, Media Officer, Unversity of Adelaide. Phone: +61 8 8313 6341, Mobile: +61 (0)410 689 084,

University of Adelaide

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