It doesn’t necessarily follow that a film that fails Bechdel doesn’t have two fully developed female characters; they just may not have a scene together. Also the requirement of “not about a man” is open to interpretation.
I agree with others that it’s a nice rule for making a general point, but there are lots of films that fail the test and nonetheless present a positive view of women.
I constructed a dataset from 1936 to now from the webpage. (N>=10, each year). It’s noisy, though the fluctuations decline as the number of movies per year increases.
My 2 series were “Share of movies listed with less than 2 women” and “Share of movies that pass the Bechdel test”. To deal with the noise, I added a 5 year centered moving average. Here’s the 3 part chart: http://wm40.inbox.com/thumbs/7d_130b41_d2595_oP.png.thumb
There appear to have been pro-Bechdel fads in the early part of the era. But methinks the first sustained tendency towards more female inclusive films was from 1980-1986. The 1990s also showed some positive trends. We’re now somewhere north of 60%, which isn’t especially high.