Participation Inequality and the 90-9-1 Principle in Open Source.

Participation inequality is a major challenge in any shared-resource system. This is known as the "volunteer's dilemma": everybody wants to benefit from a resource without contributing, expecting others will do the work. This paper explores whether this problem also arises in open source development. In particular, we analyze the behaviour of GitHub users to assess whether the 90-9-1 principle applies to open source. We study it both from a qualitative (ratio of activity types) and a quantitative (total number of activities) perspective and we show that the principle does not hold if we consider the GitHub platform as a whole. Surprisingly, results are reversed depending on the specific projects we look at. We believe these results are useful to project managers to better understand and optimize the behaviour of the community around their projects and, as a side effect, they show the importance of diversity in sample selection.