It's pretty obvious that one of the many problems in studying history by relying on the print record is that writers of books are disproportionately male.
Data can give some structure to this view. Not in the complicated, archival-silences filling way--that's important, but hard--but just in the most basic sense. How many women were writing books? Do projects on big digital archives only answer, as Katherine Harris asks, "how do men write?" Where were gender barriers strongest, and where weakest? Once we know these sorts of things, it's easy to do what historians do: read against the grain of archives. It doesn't matter if they're digital or not.
One of the nice things about having author gender in Bookworm is that it opens a new way to give rough answers to these questions. Gendered patterns of authorship vary according to social spaces, according to time, according to geography: a lot of the time, the most interesting distinctions are comparative, not absolute. Anecdotal data is a terrible way to understand comparative levels of exclusion; being able to see rates across different types of books adds a lot to the picture.
More interesting findings might come out of more complicated questions about interrelations among all these patterns: lots of questions are relatively easy to answer with the data at hand. (If you want to download it, it's temporarily here. For entertainment purposes only, etc., etc.)
The most basic question is: what percentage of books are by women? How did that change? (Of course, we could flip this and ask it about men--this data analysis is going to be clearer if we treat women as the exceptional group). Here's a basic estimate: as the chart says, post-1922 results are unreliable. The takeaway: something like 5% at midcentury, up to about 15% by the 1920s.