Interesting new study (PDF) from Stefano DellaVigna of UC Berkeley and Johannes Hermle of the University of Bonn. From the abstract (emphasis mine):

Media outlets are increasingly owned by conglomerates, inducing a conflict of interest: a media outlet can bias its coverage to benefit companies in the same group. We test for bias by examining movie reviews by media outlets owned by News Corp. — such as the Wall Street Journal — and by Time Warner — such as Time.

We use a matching procedure based on reported preferences to disentangle bias due to conflict of interest from correlated tastes. We find no evidence of bias in the reviews for 20th Century Fox movies in the News Corp. outlets, nor for the reviews of Warner Bros. movies in the Time Warner outlets. We can reject even small effects, such as biasing the review by one extra star (out of four) every 13 movies. We test for differential bias when the return to bias is plausibly higher, examine bias by media outlet and by journalist, as well as editorial bias. We also consider bias by omission: whether the media at conflict of interest are more likely to review highly-rated movies by affiliated studios.

In none of these dimensions do we find systematic evidence of bias. Lastly, we document that conflict of interest within a movie aggregator does not lead to bias either.

(For an interesting and somewhat contradictory perspective, you might enjoy this great piece from the summer on the history of Entertainment Weekly and its role within the various iterations of Time Warner.)

So why don’t movie reviews get skewed to support the corporate parent? DellaVigna and Hermle suggest it’s the high degree of competition: “We conclude that media reputation in this competitive industry acts as a powerful disciplining force.” In other words, there are plenty of voices available on any given movie, so readers who think the fix is in for Horrible Bosses 2 would find it easy to switch to some other source of reviews.

(I’d argue another factor is that inaccurate movie reviews exact a more concrete cost to readers — a wasted movie ticket and a lame night out — than most other news products. You generally don’t lose money and time if a city council story has a fact wrong. That direct tie to consumer behavior probably incentivizes more ready switching.)

If competition on a given subject discourages bias, you can imagine the opposite would be true too — less competition, more bias. You can certainly read that as discouraging: After all, there are many beats that have fewer professional reporters covering them than 10 or 20 years ago. But you could also read it as encouraging, since social media and personal publishing can bring corrective voices to the fore. In all cases, it seems to be a critical mass of interested voices that can help tamp down (or at least surface) bias.