Turnover is inevitable. Developers leave a project and others join it. And this effect may be more harmful in open source communities than in companies. Depending on the community, it is hard to find new people willing to participate. And even more, there is a knowledge gap left by those that gave up developing. So the issue is double: people leave and those leave a knowledge gap that in some cases is hard to fill.

However, is it possible to analyze that regeneration of developers? How good is my community retaining developers? Is it possible to measure the number of newcomers joining the community? It is clear that having this type of information is basic to define policies to attract new members, retain current ones and check if the current situation is driving the community to good terms.

This post is an example of the type of things that in Bitergia we are building on top of the CVSAnalY tool. In previous posts we introduced the concept of commit, its peculiarities as a metric, and several ways to calculate this, adding filters such as bots, merges or branches.

The demographics of open source communities allows us to understand how the community has evolved, and potentially how this community will evolve through the time. Demographics in open source communities can be seen as the typical analysis of pyramids of population in countries or cities. Typically on the top of the chart the oldest people are found, while the age decreases going to the bottom of the chart. Those are named as pyramids given their typical triangle shape. However during the last decades and in developed countries, this shape is moving to an inverted pyramid, although this is another discussion :).

Thanks to the study of the demographics of developers, it is possible to know a bit more about the community. We already introduced the demographics of the Linux Kernel, and this post is focus on the analysis of the OpenStack community as a case study. The following figure shows the demographics of the OpenStack community (daily updated in the OpenStack activity dashboard). The x-axis indicates the number of developers, while the y-axis  shows the timeframe of activity.

Green bars show the number of developers that in each of the periods started contributing with at least one commit. And blue bars show the number of those developers that still contribute to the community. By definition, a developer is still contributing to the community if a commit has been detected during the last six months. If not, this developer is considered as a developer that left the community. There may raise the case when a developer after more than six months, returns and submit another change to the source code. In this specific context, this developer would appear as not leaving the community.

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