Matching Skills, Past Collaboration, and Limited Competition: Modeling When Open-Source Projects Attract Contributors

Attracting and retaining new developers is often at the heart of open-source project sustainability and success. Previous research found many intrinsic (or endogenous) project characteristics associated with the attractiveness of projects to new developers, but the impact of factors external to the project itself have largely been overlooked. In this work, we focus on one such external factor, a project's labor pool, which is defined as the set of contributors active in the overall open-source ecosystem that the project could plausibly attempt to recruit from at a given time. How are the size and characteristics of the labor pool associated with a project's attractiveness to new contributors? Through an empirical study of over 516,893 Python projects, we found that the size of the project's labor pool, the technical skill match, and the social connection between the project's labor pool and members of the focal project all significantly influence the number of new developers that the focal project attracts, with the competition between projects with overlapping labor pools also playing a role. Overall, the labor pool factors add considerable explanatory power compared to models with only project-level characteristics.