The Social Dynamics of Reddit
 Part 2: Who sticks around?

Communities vs. crowds

In Part 1 of my examination of the social dynamics of Reddit, I considered the difference between groups that look like audiences (in which very few group members account for the majority of comments in group discussions) and groups that look more like true communities (in which participation is more evenly dispersed among all group members). In Part 2, I consider another aspect of group dynamics: the extent to which group members stick around and participate in discourse continuously. 

The idea here is that the social bonds indicative of community tend to take time to develop. If there is a high "turnover" or "churn" among group members, the group may have an outward appearance of stability (i.e., the group may maintain a steady overall number of participants from month to month) while never creating the conditions under which lasting social bonds and knowledge of one's fellow member are likely to take root. Such a group would be more like a crowd than a community. Think of the crowds that cycle through tourist destinations like Times Square in New York City. Are the online groups we see on Reddit more analogous to these kinds of fleeting configurations of people?

There are a few ways we could refer to this concept. Groups that rapidly cycle through members could be said to have a high rate of churn, a high turnover, low retention, or low "stickiness." There are also a few ways we could try to measure this. One way would be to determine what percent of members of a group who participate in a given month fail to return to participate in the following month (month-to-month churn). 

When we compare commenting behavior over the last decade among various topic-based groups (subreddits) on Reddit, we find variation in month-to-month churn, both in the average month-to-month churn of those subreddits and how that rate of churn changes over time. As we did when considering dispersion of participation among group members, we included the size of the community (number of unique commenters, or "UCs") in our visualization.

For example, let's consider churn in r/food, a subreddit dedicated to discussions relating to (obviously) food. Along the left side of the graph, you'll see "Churn," ranging from 0 (a loss of 0% of commenters from one month to the next) to 1 (a loss of 100% of commenters from one month to the next). Along the right side of the graph, you'll see "UC" (the number of unique commenters in a given month for this subreddit). 

At the start, r/food loses a little more than half of its commenters from month to month. As it grows over time, it starts to lose a greater number of commenters from month to month, though it's worth noting that the significant growth it experienced in 2014 was not accompanied by a corresponding uptick in churn. Rather, churn increased at a relatively steady rate over time. 

It turns out this pattern is fairly common, especially among a certain type of the 30 popular subreddits we analyzed: mid-size subreddits dedicated to particular hobbies or interests, e.g., books, art, music. Might this increasing churn be an inevitable consequence of time or increasing group size? 

As you can see in this graph of r/funny, some subreddits are able to have lower churn and maintain that lower churn despite significant growth. What might account for this? For starters, r/funny is a far larger group than r/food, r/books, or r/Art. For another (and, perhaps, related to its popularity), its topic is a bit more general. If we take a look at another large subreddit with a similarly general topic, r/videos, we see a similar pattern.

Then, there are the hard-to-categorize subreddits, the subreddits that are not based around links to content on other websites but rather serve exclusively as sites of discourse: r/AskReddit (a subreddit on which Reddit users pose questions to other users as a way to start a discussion or share stories) and r/IAmA (a subreddit used to collectively interview people). 

The pattern in r/AskReddit looks very similar to that observed in other larger subreddits: low, stable churn. This lends some credence to the belief that larger subreddits are more stable in terms of retaining commenters from month to month.

r/IAmA shows a different pattern: despite shrinkage, churn continues to increase over time. At least in some cases, growth and churn appear to be independent of one another (or, at the very least, not positively related to one another). 

Our research team is still in the process of analyzing the relationships among group size, distribution of participation, and churn across time within a variety of subreddits. In the meantime, feel free to explore relationships between between time, size, and churn within 30 subreddits below.

Thanks to Felipe Hoffa (u/fhoffa) for making Reddit comment data available for analysis using Google Query, and thanks to Jamie Witter for Tableau advice. Data analyzed by Conor Hollenbach, Tyler Rhodes, and Jinjie Yang at the University of Alabama.