Online radicalisation is effective: Viewing online content is related to extremist attitudes.

Dr Andrew Evelo1, Ms Taryn Farr1, Dr Maryanne Garry1

1University of Waikato


After an incident of terrorism, investigators often find that the perpetrators had viewed extremist material online. Indeed, the existing qualitative literature builds a case for the idea that the internet helps to create radicalisation. Several studies suggest that online propaganda has encouraged the spread of extremism (Drevon, 2016; Koehler, 2014). A subsequent review of this literature concluded that viewing online extremist content is associated with extremist attitudes (Hassan et al., 2018).

But the literature, and therefore investigators, lack any quantitative measures of the size of this relationship—a finding fundamental to addressing the issue. Therefore, we set out to fill this important gap by quantitively estimating the relationship between viewing online extremist materials and radicalisation.

We found eight relevant studies that reported 11 independent effect sizes. In every study, the summary statistic showed a positive correlation between exposure to online materials and radicalisation. The overall summary effect size was small, but significant, r = 0.18, 95% CI [0.14, 0.21], z = 10.39, p < .001.

These results fit with the idea that exposure to online extremist material provides a platform for extremist groups radicalise other people. But most of the studies were correlational, a factor that limits causal conclusions; we now need experimental research, using social psychological paradigms, to establish causality. In the meantime, our findings provide evidence that the Internet is a key part of the radicalisation process, at some level, and that counter-terrorism strategies and policies should take practical steps to target the spread of radical materials online.


Dr Evelo graduated in 2020 with a PhD from John Jay College of Criminal Justice, City University New York. His research on the overlap between social psychology and the law is published in journals such as Law and Human Behavior, Applied Cognitive Psychology, Journal of Experimental Psychology: Applied, and Psychology, Public Policy, and Law. He is currently a postdoctoral researcher at Waikato and the Department of Internal Affairs, investigating online radicalisation and violent extremism.