This was a follow-up to my initial look at the breakdown of various categories on AO3. After posting that, I realized that the relationship categories on AO3 were not mutually exclusive; the same fanwork could have multiple relationship tags. I redid the analysis, this time looking at all possible relationship tagging combinations.
Using the Work Search page on AO3, I selected every possible combination of relationship category checkboxes. I recorded the number of works returned by the search. (I believe I was logged in, but I am not sure; it makes a difference as to how many fanworks you can see.)
I also included a “No relationships” category in my analysis, for fanworks that don’t have any relationship category marked (this excludes “Gen” as well — it’s really more like “No relationship category tags”).
RESULTS AND DISCUSSION
M/M is the largest category on AO3 by far. (This may contrast with Fanfiction.net and other platforms, based on some cross-platform comparisons I did in the Sherlock fandom.) Possibly surprisingly, Gen is the next largest category, followed by F/M. All other categories and combinations of categories comprise less than 5% apiece.
In separate analyses, I looked at some F/F stats: