  We analyse the relation between the emotions and the activity of contributors
in the Open Source Software project Gentoo. Our case study builds on extensive
data sets from the project's bug tracking platform Bugzilla, to quantify the
activity of contributors, and its mail archives, to quantify the emotions of
contributors by means of sentiment analysis. The Gentoo project is known for a
period of centralization within its bug triaging community. This was followed
by considerable changes in community organization and performance after the
sudden retirement of the central contributor. We analyse how this event
correlates with the negative emotions, both in bilateral email discussions with
the central contributor, and at the level of the whole community of
contributors. We then extend our study to consider the activity patterns on
Gentoo contributors in general. We find that contributors are more likely to
become inactive when they express strong positive or negative emotions in the
bug tracker, or when they deviate from the expected value of emotions in the
mailing list. We use these insights to develop a Bayesian classifier that
detects the risk of contributors leaving the project. Our analysis opens new
perspectives for measuring online contributor motivation by means of sentiment
analysis and for real-time predictions of contributor turnover in Open Source
Software projects.
