Who reads more books?

I'm not going to make this blog about politics, but this tidbit was too tantalizing to pass up. Apparently, liberals read more books than conservatives. Alas, the sample size (about 1000 people) was too small to ask more detailed questions. Is there a difference between how much fiction and how much non-fiction each group reads? What about literary versus genre fiction?

Did the study control for factors known to affect political allegiance, and also known to influence reading habits? For instance, people who are affluent and well-educated are slightly more like to vote Democrat. Women are also slightly more likely than men to identify as Democrats. It happens that affluent, well-educated people read more than those lacking those advantages. (It's worth noting, however, that a French study found a love of reading can help low-income students catch up academically with their more privileged peers.) And women read more than men. In fact, it's been claimed, "When women stop reading, the novel will be dead."

The same article reported, "Among avid readers surveyed by the AP, the typical woman read nine books in a year, compared with only five for men. Women read more than men in all categories except for history and biography."

Compare this with the political literary divide: "Among those who had read at least one book, liberals typically read nine books in the year, with half reading more than that and half less. Conservatives typically read eight, moderates five."

If all those other factors were controlled for, would political leanings alone still indicate a difference in reading habits?