On Reddit, one metric is often used to communicate a subreddit's size, it's influence, and, for lack of a better word, it's "health": the number of subscribers.
Reddit users subscribe to subreddits to become regular consumers of its content (posts) and discourse (comments). In this sense, subscribers are somewhat similar to "followers" on other sites or "audiences" in traditional media contexts. If a user didn't like the posts or comments they were seeing from the subreddit, they would unsubscribe. We can infer that if the content posted to a subreddit were to decline (that is: fail to be of interest to its subscribers), then it's subscriber count would decline.
But what happens if the content's quality doesn't decline but the content quantity does? Put another way, what happens when the content and comments of a subreddit simply "dry up?"
Subscribers might not even notice the decline in content quantity, or might notice it but accept the reality that there just isn't as much to post about in that subreddit. Thus, they may not go to the trouble of unsubscribing, leaving the impression that the subreddit is still as large, influential, and "healthy" as it once was. To take an extreme example, think of a subreddit related to a specific event in time. Many users may subscribe to it in the lead up to that event, and once the event has passed, they may not bother to unsubscribe. Their subscription to that subreddit does not take up any space in their feed, so there is little reason to bother to unsubscribe. To take a less extreme example, consider a once-lively broad category subreddit that was simply superceded by more specific, newer subreddits. Commenters and posters may have migrated away, but the subscriber count would stay frozen where it is, or might even increase if it was among the default subreddits to which new users were automatically added.
How common is it for popular subreddits to stagnate in this way: to decline in comments and posts counts while maintaining a large number of subscribers?
Reddit users subscribe to subreddits to become regular consumers of its content (posts) and discourse (comments). In this sense, subscribers are somewhat similar to "followers" on other sites or "audiences" in traditional media contexts. If a user didn't like the posts or comments they were seeing from the subreddit, they would unsubscribe. We can infer that if the content posted to a subreddit were to decline (that is: fail to be of interest to its subscribers), then it's subscriber count would decline.
But what happens if the content's quality doesn't decline but the content quantity does? Put another way, what happens when the content and comments of a subreddit simply "dry up?"
Subscribers might not even notice the decline in content quantity, or might notice it but accept the reality that there just isn't as much to post about in that subreddit. Thus, they may not go to the trouble of unsubscribing, leaving the impression that the subreddit is still as large, influential, and "healthy" as it once was. To take an extreme example, think of a subreddit related to a specific event in time. Many users may subscribe to it in the lead up to that event, and once the event has passed, they may not bother to unsubscribe. Their subscription to that subreddit does not take up any space in their feed, so there is little reason to bother to unsubscribe. To take a less extreme example, consider a once-lively broad category subreddit that was simply superceded by more specific, newer subreddits. Commenters and posters may have migrated away, but the subscriber count would stay frozen where it is, or might even increase if it was among the default subreddits to which new users were automatically added.
How common is it for popular subreddits to stagnate in this way: to decline in comments and posts counts while maintaining a large number of subscribers?
SUBSCRIBERS VS. COMMENTS, OVER TIME
One useful starting point to answering this question would be to look at subreddits that achieved a high number of subscribers and follow the relationship between subscribers and comments over time. Just looking at the Top 20 subreddits in terms of subscribers shows that the relationship between subscribers and comments varies greatly across subreddits. Some subreddits have always had very few comments, either because they are tightly moderated and only allow very specific types of comments (e.g., r/science), or because the type of content they showcase simply doesn't inspire much commentary (r/EarthPorn). To get a sense of a subreddit's level of engagement, we need to look at how the relationship between subscriber count and comment count changes over time, and whether it diverts from its own internal norm or baseline.
PATTERNS
In the graphs below, each dot represents a year in the life of the subreddit, starting in 2012 on the left and moving to 2020 on the right. Number of subscribers are on the X axis and number of comments are on the Y axis.
One clear pattern among the most subscribed-to subreddits is that they tend to add subscribers over time. This may have more to do with the growing size of Reddit generally: as more new users arrive, the subscriber counts of most popular subreddits increase. The use of default subreddits and the presence of most of these popular subreddits among them is an obvious explanation for this: new Reddit users were added to the subscriber counts of these subreddits by default.
The relationship between subscribers and comments over time varies among subreddits. In the case of some subreddits, such as r/worldnews, the comment count increases at roughly the same rate as the subscriber count. This seems like pretty clear evidence of a community in which engagement increases as audience size increases.
One clear pattern among the most subscribed-to subreddits is that they tend to add subscribers over time. This may have more to do with the growing size of Reddit generally: as more new users arrive, the subscriber counts of most popular subreddits increase. The use of default subreddits and the presence of most of these popular subreddits among them is an obvious explanation for this: new Reddit users were added to the subscriber counts of these subreddits by default.
The relationship between subscribers and comments over time varies among subreddits. In the case of some subreddits, such as r/worldnews, the comment count increases at roughly the same rate as the subscriber count. This seems like pretty clear evidence of a community in which engagement increases as audience size increases.
In other cases, such as r/todayilearned, the comment rises at first but then plateaus, staying roughly the same even as the subscriber count rises. This may suggest that the subreddit has a natural level of engagement that, once reached, can only be maintained but not exceeded.
In other cases, such as r/videos, comments increase as subscribers increase for a time, but then decline. This is evidence that a subreddit is, in terms of engagement, "past its prime." In the case of general-topic subreddits like r/videos and r/gifs, they may have been superceded by more specific subreddits (e.g., r/reactiongifs, r/BeAmazed, etc.).
Other popular subreddits, such as r/funny or r/gaming, don't exhibit such clear patterns: the numbers of comments fluctuate from year to year. It's hard (for me, at least) to think of a reason why the number of comments in r/funny would decline one year and not the next. It's interesting to consider the degree of volatility in comment counts from year to year. Like so many things on Reddit, it may be idiosyncratic, unique to particular communities of topics.
This interactive graph allows you to explore the relationships between time, subscriber counts, and comment counts across the 20 most highly subscribed subreddits (as of April 2021). You can compare different subreddits by checking or unchecking the boxes on the right and moving through the years by selecting years in the drop-down menu.
Thanks to Jason Baumgartner for making Reddit data available on redditsearch.io, to frontpagemetrics.com, and to Matthew Gaines and the rest of the ARRG team at the University of Alabama.