Noname manuscript No. (will be inserted by the editor) The Promises and Perils of Mining GitHub

the date of receipt and acceptance should be inserted later Abstract With over 10 million git repositories, GitHub is becoming one of the most important sources of software artifacts on the Internet. Researchers mine the information stored in GitHub’s event logs to understand how its users employ the site to collaborate on software, but so far there have been no studies describing the quality and properties of the available GitHub data. We document the results of an empirical study aimed at understanding the characteristics of the repositories and users in GitHub; we see how users take advantage of GitHub’s main features and how their activity is tracked on GitHub and related datasets to point out misalignment between the real and mined data. Our results indicate that while GitHub is a rich source of data on software development, mining GitHub for research purposes should take various potential perils into consideration. For example, we show that the ma-This work is an extended version of Kalliamvakou et al (2014b), published at the Interna-tional Working Conference on Mining Software Repositories, MSR 2014. The extension falls into two categories. First, we have identified four additional perils: two are related to the information about GitHub users and two are related to the information that GitHub makes available. Second, we have assessed the perils ’ potential impact as threats to validity on selected studies