Media bias explained | A biased market

Showing that newspapers have a political slant that is economically rational does not necessarily answer the question of whether ownership or demand determines bias. Here, the academics are helped by the fact that large media companies may own several newspapers, often in markets that are politically very different. This allowed them to test whether the slants of newspapers with the same owner were more strongly correlated than those of two newspapers picked at random. They found that this was not so: owners exerted a negligible influence on slant. Readers’ political views explained about a fifth of measured slant, while ownership explained virtually none.

Media bias explained | A biased market | The Economist