Evidence for the Pareto principle in Open Source Software Activity

Numerous empirical studies analyse evolving open source software (OSS) projects, and try to estimate the activity and effort in these projects. Most of these studies, however, only focus on a limited set of artefacts, being source code and defect data. In our research, we extend the analysis by also taking into account mailing list information. The main goal of this article is to find evidence for the Pareto principle in this context, by studying how the activity of developers and users involved in OSS projects is distributed: it appears that most of the activity is carried out by a small group of people. Following the GQM paradigm, we provide evidence for this principle. We selected a range of metrics used in economy to measure inequality in distribution of wealth, and adapted these metrics to assess how OSS project activity is distributed. Regardless of whether we analyse version repositories, bug trackers, or mailing lists, and for all three projects we studied, it turns out that the distribution of activity is highly imbalanced.