## 4 Dataset Description  
Before presenting our use of the proposed method in the analysis of online communities, we provide a detailed description of the datasets used. We collected articles with attached comments from three online communities (Reddit, Slashdot, and PGR21) as in Table 3.  
Reddit is one of the largest online communities in the United States, and it consists of a number of subcommunities called subreddits, among which we selected two subreddits: \(r\)/politics and \(r\)/AskReddit. Our reason for selecting these is two-fold. They are both popular subreddits with a large number of active users. In subreddit \(r\)/politics, the main topic is political issues, as its name indicates, and on average more than 650 articles are posted per day. In the dataset we collected, more than 209 k users participated in the articles, leaving a total of 4.1 M comments. In \(r\)/AskReddit, questions across a variety of fields, ranging from \"personal stuff\" to serious social problems, are uploaded, and users answer and discuss the questions they are interested in. There are 5 k articles per day on average, in which 1.2 M users leave a total of more than 13 M comments. The users in these two subreddits display different behaviors. The user interaction in \(r\)/politics is observed to be more intensive than that in the AskRedit subreddit. The number of articles receiving more than 10 comments in \(r\)/politics is 63.8% of all articles, while only 40.4% of articles in \(r\)/AskReddit achieved this. About 7% of users leave at least 50 comments in \(r\)/politics, while the portion of such users in \(r\)/AskReddit is only 3.6%.  
Slashdot is a discussion-centric community with a moderate scale. This community supports many functionalities, such as categorization and comment-rating systems, to encourage intensive and constructive discussion across a variety of topics. The average number of articles posted per day is about 20, which is considerably smaller than for the Reddit datasets. Due to this difference in scale, we collected articles over 3 years from Slashdot, while the duration of the Reddit dataset is about 3 months. However, this difference in article generation rates provides another perspective on community characteristics. User participation in Slashdot is more active as the exposure of each individual article lasts much longer, and almost all articles have at least 10 comments, while about 36% of the articles in \(r\)/politics have less than 10 comments.  
PGR21 is another moderate-scale community in South Korea, which also has a relatively low article generation rate, less than 20 articles per day. We collected articles from PGR21 freeboard for 3 years. This community is not as dedicated to discussion as Slashdot is. Users can post articles on any topic, ranging from \"mild\" stories of everyday life to controversial political issues. However, some community rules (for example each article should contain a certain amount of personal opinion from  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**id** & **Community** & **Articles** & **Comments** & **Users** & **Period** \\ \hline R1 & Reddit \(r\)/politics & 56 K & 4.1 M & 209 K & Mar 2018–Jun 2018 & (\(\approx\)83 days) \\ R2 & Reddit \(r\)/AskReddit & 483 K & 13.6 M & 1.2 M & Mar 2018–Jun 2018 & (\(\approx\)91 days) \\ SD & Slashdot & 22 K & 3.5 M & 33.7 K & Jan 2015–Dec 2017 & (3 years) \\ PG & PGR21 & 17 K & 975 K & 9.1 K & Jan 2015–Dec 2017 & (3 years) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Datasets used in this paper.  
the article uploader), and a relatively longer exposure of articles (about 2-3 days on the front page), encourage users to actively communicate with each other, which sometimes leads to intense discussion.