Republicans Smarter than Democrats?

Republicans outscore Democrats in political knowledge, according to this Pew report.  However, this comes with some caveats:

Republicans, on average, answered one more question correctly than Democrats (5.9 vs. 4.9 correct). These differences are partly a reflection of the demographics of the two groups; Republicans tend to be older, well educated and male, which are characteristics associated with political and economic knowledge. 

Okay, so maybe if you control for age, education, and sex, then all will be equal?  Not necessarily, the Pew folks say:

Still, even when these factors are held constant, Republicans do somewhat better than Democrats on the knowledge quiz.

In other words, Republicans are smarter even if you hold age, education, and sex constant.  But what if you hold constant, statistically, a host of other factors that may also explain what people know?  There are some socio-demographic factors you can toss in the model (race being one politically incorrect one, income being another) that will also explain some of the variance, probably enough to even out partisan differences.  But you have to ask, what's the point?  If these political and social differences are what make up partisan alignment, then controlling for those very same factors to "even out" the differences doesn't make a lot of sense.  Let's just agree that the people who consider themselves Republicans score higher on tests of political knowledge than those who consider themselves Democrats.

Below is one table from the Pew report.  Go to the link above to see the entire report.