Media bias in politics has always been a topic of interest because it is a subject everyone feels a little passionate about. Most people who pay attention to politics have an opinion about media outlets and how they possibly sway public opinion. Interestingly, no matter who you select, they believe the media always favors the other candidate, party, ideology, etc. In the USA, liberals say the media is conservative \cite{Dennis:Liberal:1996} and conservatives say the media is liberal \cite{Bozell:How:1992}. Who is right?

In 2000, D'Alessio and Allen \cite{DAlessio:2000te} set out to answer the question above. They investigated 3 kinds of bias namely: {\it gatekeeping bias}, the preference for selecting stories about one party or the other; {\it coverage bias}, or the amount of coverage each party gets; and {\it statement bias} which deals with the favorability of coverage towards one party. The authors looked at bias in newspapers, magazines and television and of these only the television had a slight coverage bias and statement bias.

Druckman and Parkin \cite{druckman2005impact} showed that the effect of a newspaper tone towards a candidate can impact the voters' decision and they found some good evidence that the slanted editorials indeed can achieve this goal. They also raised the question of whether readers are to blame or the victims for not looking for diversity in their media activities (reading, watching TV, etc.)

Groseclose and Mulyo \cite{Groseclose:2005wg} have proposed an interesting measure of media bias and applied it to print and television media outlets. Their metric is based on a count of mentions to specific think tanks. Think tanks themselves are assigned a score from conservative to liberal based on the mentions of their names by members of congress. The starting point is the ADA metric (Americans for Democratic Actions) of members of congress, which is used to calculate an ADA-like for each think tank which will then be used to calculate another ADA-like score for the media outlets. The authors found that most media outlets are left-leaning (liberal), except for the Fox News' Special Report and the Washington Times.

Media bias may also be related to voting patterns. DellaVigna and Kaplan \cite{dellavigna2007fox} have done a study specifically with the Fox News Channel in more than 9,000 towns in the USA and found that their pro-right approach accounted for a significant gain of the republican party between the years 1996 and 2000. On average the party gained 0.4 to 0.7 percentage points in the towns where the Fox News Channel was available.

Nowadays we live in the decade of the big data. Scientists today have the ability to collect data about virtually anything and certainly politics is one area of interest. This availability should yield more reliable results on bias, be it on politics or any other issue worth studying.