  Continuous integration is a software engineering practice of frequently
merging all developer working copies with a shared main branch, e.g., several
times a day. With the advent of GitHub, a platform well known for its "social
coding" features that aid collaboration and sharing, and currently the largest
code host in the open source world, collaborative software development has
never been more prominent. In GitHub development one can distinguish between
two types of developer contributions to a project: direct ones, coming from a
typically small group of developers with write access to the main project
repository, and indirect ones, coming from developers who fork the main
repository, update their copies locally, and submit pull requests for review
and merger. In this paper we explore how GitHub developers use continuous
integration as well as whether the contribution type (direct versus indirect)
and different project characteristics (e.g., main programming language, or
project age) are associated with the success of the automatic builds.
