Table 1.
Users distribution by Stack Overflow privileges.
Fig 1.
Number of posts and active users on Stack Overflow in each month from August 2008 to December 2020.
Plot displays the number of questions and answers posted (left axis), and the number of users creating posts or receiving score via up-votes (right axis).
Fig 2.
Trends in tag popularity: Programming languages.
Fig 3.
Trends in tag popularity: Web programming frameworks.
Fig 4.
Trends in tag popularity: Operating systems.
Table 2.
Network metrics of the detected communities.
Fig 5.
Stack Overflow community graph.
User-tag interaction graph created from all available data between 2008 and 2020. Left: Communities of users within the Stack Overflow platform. Right: Tag clouds corresponding to each community showing the most frequent tags used by the users in that community.
Fig 6.
Evolution of the Stack Overflow communities from 2008 to 2014.
Each circle shows a tag cloud with the most popular tags in a community identified in a given year. The size of the circles is somewhat proportional to the actual size of the communities, with some adjustments for layout.
Fig 7.
Evolution of the Stack Overflow communities from 2015 to 2020.
Each circle shows a tag cloud with the most popular tags in a community identified in a given year. The size of the circles is somewhat proportional to the actual size of the communities, with some adjustments for layout.
Table 3.
Community characterisation.
Fig 8.
Movement of users in/out/within Stack Overflow.
The top node indicates the flow of new users into the platform (users that were not present in the previous year). The second node indicates flows of users that become inactive (i.e. do not acquire any score on the next year), migrate to another community within the platform, or stay in the same community in consecutive years.
Fig 9.
Heat map of year-to-year pairwise similarity of community membership.
The heat map displays the average percentage overlap of users belonging to each pair of communities in consecutive years between 2008 and 2020. Diagonal entries indicate self-similarity and community persistence. Off-diagonal entries indicate flows between communities.
Fig 10.
Evolution of community sizes over time.
The time series present the percentage of all users on Stack Overflow that each detected community contains in each year from 2008 to 2020. Plots for the 15 largest communities are shown, smaller communities are omitted for clarity.