The study, published in the European Economic Association, investigated how negative rhetoric about refugees on social media may have contributed to hate crimes against refugees in Germany between 2015 and 2017.

"We think our paper can only be a starting point for understanding how social media causes changes in our lives. Our findings on hate crime suggest that the stakes are high," said study author Karsten Müller from Princeton University in the US.

In Germany, social media is among the main news sources of 18 to 25-year-olds. In the US, around half of all adults use social media to get news and two-thirds of Facebook users use it as a news source.

In contrast to traditional media, social media platforms allow users to easily self-select into niche topics and extreme viewpoints.

This may limit the range of information people absorb and create online communities that reinforce similar ideas and viewpoints.

The researchers measured anti-refugee sentiment on social media based on the Facebook page of the Alternative für Deutschland, a relatively new right-wing party that positions itself as anti-refugee and anti-immigration.

The party is by far the most popular far-right political movement in Germany and with more than 300,000 followers, 175,000 posts, 290,000 comments, and 500,000 likes (as of early 2017), its Facebook page has a broader reach than that of any other German party.

As the researchers show, the rhetoric about refugees on the Alternative für Deutschland Facebook page differs markedly from traditional news sources and in many cases contains language that prominent German non-governmental organisations have classified as hate speech.

The researchers established that spikes in posts about refugees on social media are tightly linked to anti-refugee hate crimes, particularly in municipalities where people were more exposed to the Alternative für Deutschland page.

This correlation was especially pronounced for violent incidents such as assault.

Municipalities with Alternative für Deutschland users were three times more likely to experience an attack during the observation period.

Out of the total 3,335 attacks on refugees in the same sample, 3,171 occurred in municipalities with Alternative für Deutschland Facebook page users.

The authors found that, while anti-refugee attacks increased with anti-refugee posts, this relationship disappeared during the internet or Facebook outages.

The researchers do not claim that social media itself causes crimes against refugees. Rather, the results suggest that social media can help propagate violent crimes by enabling people to spread extreme viewpoints.