It's confirmed on a national basis now. Fox News really does make you dumber, as if those of us who have had to watch it for even a few minutes haven't figured that out. Not only does it make viewers dumber, but they'd be more informed and better off if they watched no news at all.

That's a stunning conclusion, because it proves they actually succeed at indoctrinating their audience with falsehoods. Via Huffington Post, news of an updated study to the one last year, this time on a national basis:

Researchers at Fairleigh Dickinson University updated a study they had conducted in late 2011. That study only sampled respondents from New Jersey, where the university is located. This time, the researchers conducted a nationwide poll.

The poll asked questions about international news (Iran, Egypt, Syria and Greece were included) and domestic affairs (Republican primaries, Congress, unemployment and the Keystone XL pipeline.)

The pollsters found that people were usually able to answer 1.8 out of 4 questions on foreign news, and 1.6 of 5 questions on domestic news, and that people who don't watch any news were able to get 1.22 of the questions on domestic policy right.

As the study explained, though, people who watched only Fox News fared worse:

The largest effect is that of Fox News: all else being equal, someone who watched only Fox News would be expected to answer just 1.04 domestic questions correctly -- a figure which is significantly worse than if they had reported watching no media at all. On the other hand, if they listened only to NPR, they would be expected to answer 1.51 questions correctly; viewers of Sunday morning talk shows fare similarly well. And people watching only "The Daily Show With Jon Stewart" could answer about 1.42 questions correctly.

According to the study, Fox News is more likely to make conservatives dumber, proving that they reinforce factless assertions:

The study showed that the effects of ideologically-pitched media, like Fox News, MSNBC and talk radio, depend on who is listening or watching. On the whole, MSNBC, for instance, had no impact on political knowledge one way or the other. However, liberals who watched MSNBC did better on the knowledge questions, answering correctly 1.89 of the domestic questions and 1.64 of the international questions correctly. Similarly, while moderates and liberals who watch Fox News do worse at answering the questions than others, conservatives who watch Fox do no worse than people who watch no news at all. Talk radio also had differential effects depending on the ideology of the listener, but they were much smaller. None of the other news media had effects that depended on ideology.

The real bottom line? Watch Jon Stewart. Those viewers were better informed than any of the others except NPR listeners.