Social media news communities: gatekeeping, coverage, and statement bias

We examine biases in online news sources and social media communities around them. To that end, we introduce unsupervised methods considering three types of biases: selection or ``gatekeeping'' bias, coverage bias, and statement bias, characterizing each one through a series of metrics. Our results, obtained by analyzing 80 international news sources during a two-week period, show that biases are subtle but observable, and follow geographical boundaries more closely than political ones. We also demonstrate how these biases are to some extent amplified by social media.