Another "don't know" problem

When looking at the tabulations for the questions in my last post, I noticed a difference in the percent of "don't know" answers of self-described liberals and conservatives.  I then checked the others to see if the pattern persisted.  It did, and there are strong parallels between the gender and liberal/conservative differences.  I'll give the average for the eleven questions to make it simpler:

                    Correct     Incorrect      DK
Liberals              38%          33%         29%
Men                   35%          31%         33%
Conservatives         31%          28%         40%
Women                 30%          29%         41%


Liberals and men give more correct answers, more incorrect answers, and fewer don't knows.  The ratio of correct to incorrect answers is about the same in all groups (slightly higher among men and liberals).

So what's going on?  Although I still think my point about gender differences from the last post is partly correct, it seems to be incomplete.  My interpretation:
 (a) People sometimes interpret "conservative" to mean "cautious" (as I've discussed in other posts, a significant number of people seem to understand liberal and conservative in non-political senses)
(b) differences in "don't knows" don't involve people who know or have no idea, but people who "sort of" know, or could make a fairly good guess.  Conservatives and women who are in that middle group may be less likely to venture an answer.

Some insight is provided by the question:   "Which one of the following people is not a college dropout:   Facebook founder Mark Zuckerberg, designer Ralph Lauren, entertainer Ellen Degeneres, Apple founder Steve Jobs, President Calvin Coolidge, movie mogul David Geffen, and oil magnate John D. Rockefeller?"
It seems safe to assume that very few people definitely knew the true answer or confidently believed an incorrect answer.*  But you could apply some pieces of common knowledge (e. g., that a lot of people who became rich from computers or the internet were college dropouts) to make an educated guess.   So the group differences in "don't knows" were essentially a matter of willingness to try.  

                    Correct     Incorrect      DK
Liberals              20%          43%         27%
Men                   14%          53%         33%
Conservatives          8%          50%         42%
Women                 11%          44%         45%

Men were more willing to try than women, but there was little or no difference in the probability of getting it right if they tried.  Conservatives were less willing to try than liberals. Given the fairly small number of liberals and large number of don't knows, the liberal/conservative differences in the conditional probability of getting it right, although large, are not statistically significant.  

*Coolidge graduated from Amherst College, so I count him as the correct answer.  I'm not sure it's accurate to call Rockefeller a college dropout--see his biography here--but he didn't have a college degree.