A survey by PIPA (Program on International Policy Attitudes) came up with some surprising and dramatic results.
Respondents were asked three questions about Iraq:
1. Since the war with Iraq has ended, is it your impression that the U.S. has or has not found Iraqi weapons of mass destruction?
2. Is it your impression the Iraq did or did not use chemical or biological weapons in the war that just ended?
3. Thinking about how all the people in the world feel about the U.S. going to war with Iraq, do you think: The majority of people favor the U.S. going to war?
To date, no weapons of mass destruction have been found, nor were any chemical or biological weapons used in the recent war. World opinion was not in favor of attacking Iraq.
The respondents were then asked which news sources they used.
Those who got most of their information from Fox News had the highest rate of misperceptions. Those who use NPR and/or PBS has the lowest rate.
80% of Fox respondents had at least one or more misperceptions

Only 23% of NPR/PBS respondents had one or more misperceptions.
45% of Fox viewers got
all three questions wrong.
Only 4% of NPR views missed all three.
Here's the complete report; it's in PDF format. Scroll down to page 13 and look at the chart on the left, "Frequency of Misperceptions", and the one under it.
Click me! The report admits that it can't tell which came first, the chicken or the egg -- that is, are Fox viewers more misinformed to begin with than NPR/PBS types, or did Fox News make them misinformed?
MRPLUTO