The Nature of Real and Perceived Bias in Chilean Media

News consumers expect news outlets to be objective and balanced in their reports of events. However, there is a body of evidence of bias in the media caused by underlying political and socio-economic viewpoints. Previous studies have tried to classify the partiality of the media, sometimes giving a quantitative evaluation, but there is little reported on its nature. The vast amount of content in the social media enables us to quantify the inclination of the press to either side of the political spectrum. To describe such tendencies, we use tweets to automatically compute a news outlet's political and socio-economic orientation. We show that the media have a measurable bias, and illustrate this by showing the favoritism of Chilean media for the ruling political parties in this country. We also found that the nature of the bias is reflected in the vocabulary used and the entities mentioned by different news outlets. A survey conducted among news consumers confirms that media bias has an impact on the coverage of controversial topics and that this is perceivable by the general audience. Having a more accurate method to measure and characterize media bias will clarify to the readers where outlets stand within the socio-economic landscape, even when a self-declared position is stated. This will empower readers to better reflect on the content provided by their news outlets of choice.