Follow up: I redid one of the graphs to satisfy my own interest in the question. Instead of averaging over all the movies ever released like the article did, I averaged over all the votes. This was an attempt to answer the question of whether the average viewing experience of a film from year x is better or worse than that of a film from year y.
I found that there has been a noticeable decline in the average rating of over half a point (out of 10) since ~1930 or so. https://i.imgur.com/bY9vPvk.png
I think this should be explained in a combination of two ways:
* History acts as a filter. If I choose to watch a movie from 1947 it's probably because a lot of people over the years have said it's good.
* To some extent, older movies may really be better than more recent ones.
I still suspect that the blockbuster effect means that the movies people are mostly to watch are going to receive higher ratings than the average film overall. And this is mostly because people rating blockbusters are less critical than the film-viewing community as a whole. So while there might be no "recency bias" of the kind this article was looking for, there might be blockbuster bias where in the last several decades studios have figured out how to capitalize on a less critical / cynical audience. (That hockey stick graph of 8-10 ratings in the article is certainly suggestive.)
Actually -- one more follow up for the zero people who will read this -- there's a simpler explanation, which other people who do these kinds of statistics should probably note.
The average rating between 1920 and 1980 fluctuated at about 7.5. Then the number of movies exploded, and the variability in quality of them exploded even more than that. Movies that were better than the 1980 average had their ratings compressed (you can only do a little better than 7.5 on IMDB). Movies that were worse were much less compressed (you can easily do much worse than a 7.5). So the average gets dragged down since there are now both more movies getting 0-4s and movies getting 8-10s.
I realized this after plotting the median, not the mean, and observing that it stays remarkably constant, and possibly even shows a little recency bias for the last 2 years.
I found that there has been a noticeable decline in the average rating of over half a point (out of 10) since ~1930 or so. https://i.imgur.com/bY9vPvk.png
I think this should be explained in a combination of two ways:
* History acts as a filter. If I choose to watch a movie from 1947 it's probably because a lot of people over the years have said it's good.
* To some extent, older movies may really be better than more recent ones.
I still suspect that the blockbuster effect means that the movies people are mostly to watch are going to receive higher ratings than the average film overall. And this is mostly because people rating blockbusters are less critical than the film-viewing community as a whole. So while there might be no "recency bias" of the kind this article was looking for, there might be blockbuster bias where in the last several decades studios have figured out how to capitalize on a less critical / cynical audience. (That hockey stick graph of 8-10 ratings in the article is certainly suggestive.)