[hcarvalhoalves]

Even if the data source is biased, it would be interesting to know _how_ it’s biased.

After all, it’s the data that is widely available to people on the internet.

[lillabullero]

In this particular case, it's biased because Google Books includes much more fiction and many fewer scholarly works after about the year 2000. Link to a response of a previous article by this same group: https://www.pnas.org/content/118/45/e2115010118.short