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For a year, the group reviewed the comments made on news items on four different websites.

In total, the most popular websites had 1.2 million articles and 42 million comments, which had been liked or received a thumbs down a total of 140 million times.

The research group observed that when people liked comments, the commenter generally began to add more comments to the websites. Liking  a comment did not affect the quality of the content.

The researchers also noticed that when a commenter received thumbs down symbols on their texts, this person usually began to write even more – to an even greater extent than those whose comments were liked. At the same time, negative feedback also decreased the quality of texts produced by the commenter who received negative feedback.

Since negative feedback had more impact than positive feedback, over time the possibility of providing negative feedback made discussion on all websites more negative than it was at the starting point.

Watch Leskovec's talk .