The onion has cancer: some social network analysis visualizations of open source project communication

Background: People contribute to OSS projects in wildly different degrees, from reporting a single defect once and never coming back to spending many hours each workday on the project over several years - or anything in between. It is a common conception that these degrees of participation sort the participants into a number of similar groups which are layered like the peels of an onion: The onion model. Objective: We check whether this model of gradually different degrees of participation is valid with respect to the participation in OSS project mailing-list traffic. Methods: We perform social network analysis based on replies to mailing-list messages and use visualization to check the nature of three different groups of participants. Results: There appears to be a discontinuity with respect to core members: The degree to which very active core members (as opposed to less active co-developers) react to e-mails of senders from the project's periphery is significantly higher than would be expected from their level of activity in general. Limitations: The effect might be an artifact of the assumption that each mailing-list message can be treated the same. Conclusions: We conclude that core member status may be qualitatively (rather than just quantitatively) different and the transition of individual mailing-list participants towards ever higher participation is qualitatively discontinuous.