From Technology Review:

. . . They then created a list of over 1500 websites with related content and classified each as falling into the category of favouring gun control, favouring gun rights or balanced. They also divided the websites in these categories into subsections indicating whether they were purely factual, moderate or extreme in their views.

“From the extracted on-topic web pages 25% are purely factual, 10% highly balanced, 31% and 21% moderate and extreme gun rights respectively and 9% and 4% moderate and extreme gun control,” say Koutra and co.

They then studied the browsing habits of individuals to find out the variety of information that they accessed on this topic. The results give clear evidence of the “filter bubble” at work: most users access a small number of sites, most of which fall into the same category. “All in all, people use the web to largely access agreeable information,” conclude Koutra and co.

More at the link. The penultimate paragraph of the study extract indicates their intentions; to devise ways to get partisans to read more opposing views. I’m sure this is more about getting conservatives to accept liberal views than the other way around. It always is.