Fox News is natural selection for the most credulous, least informed and most easily misinformed viewers. In other words the exact opposite of who you describe their viewership to be.
And no one will argue that there aren't at least 5.3 M people who match that profile.
STUDY: Watching Only Fox News Makes You Less Informed Than Watching No News At All
Because the aim of the study was to isolate the effects of each type of news source, they then controlled for variables such as other news sources, partisanship, education and other demographic factors.
They found that someone who watched only Fox News would be expected to answer 1.04 domestic questions correctly compared to 1.22 for those who watched no news at all. Those watching only "The Daily Show with Jon Stewart" answered 1.42 questions correctly and people who only listened to NPR or only watched Sunday morning political talk shows answered 1.51 questions correctly.