Media bias in the United States occurs when US media outlets skew information, such as reporting news in a way that conflicts with standards of professional journalism or promoting a political agenda through entertainment media. Claims of outlets, writers, and stories exhibiting both have increased as the two-party system has become more polarized, including claims of liberal and conservative bias. There is also bias in reporting to favor the corporate owners, and mainstream bias, a tendency of the media to focus on certain "hot" stories and ignore news of more substance. A variety of watchdog groups attempt to combat bias by fact-checking biased reporting and also unfounded claims of bias. Researchers in a variety of scholarly disciplines study media bias. History Before the rise of professional journalism in the early 20th century and the conception of media ethics, newspapers reflected the opinions of the publisher. Frequently, an area would be served by competing newspapers taking differing and often radical views by modern standards. In colonial Philadelphia, Benjamin Franklin was an early and forceful advocate for presenting all sides of an issue, writing, for instance, in his "An Apology For Printers" that "...when truth and error have fair play, the former is always an overmatch for the latter." From around 1790 to the late 1800s, most American newspapers were partisan. In 1798, the Federalist Party in control of Congress passed the Alien and Sedition Acts designed to weaken the opposition press. It prohibited the publication of "false, scandalous, or malicious writing" against the government and made it a crime to voice any public opposition to any law or presidential act. This part of the law act was in effect until 1801. President Thomas Jefferson, 1801–1809, was the target of many venomous attacks. He advised editors to divide their newspapers into four sections labeled "truth," "probabilities," "possibilities," and "lies," and observed that the first section would be the smallest and the last the largest. In retirement he grumbled, "Advertisements contain the only truths to be relied on in a newspaper." In 1861, Federal officials identified newspapers that supported the Confederate cause and ordered many of them closed. In the 19th century, the accessibility of cheap newspapers allowed the market to expand exponentially. Cities typically had multiple competing newspapers supporting various political factions in each party. To some extent this was mitigated by a separation between news and editorial. News reporting was expected