## 5 Discussion  
This study aimed to address two primary research questions regarding participant engagement in GitHub projects. The results for RQ1 revealed that both activity frequency and network centrality (measured by the k-core value) significantly influence a contributor's long-term participation. Participants with higher k-core values--those more central to the collaboration network--tend to remain active for longer periods. Additionally, participants who maintain frequent interactions within the project are more likely to be retained in the long term. These findings underscore the importance of not only how often participants engage but also how central their role is within the project's network structure. In response to RQ2, the analysis of PR-related behaviors indicated that participants who experience prompt PR processing and successful PR merges are more likely to remain engaged in the project. Participants with no merge experiences or who face delays in PR processing tend to reduce their participation over time. Interestingly, while the first participant (p1) plays a role in PR merging, the impact of p1's involvement on long-term participant engagement was found to be relatively minor. Additionally, while the time taken between branch creation and PR submission negatively correlates with participation duration, the time between PR submission and the creation of a new branch does not consistently affect engagement. These findings have several important implications. First, they highlight the significance of efficient PR management for participant retention. Prompt feedback and the merging of contributions not only reinforce participants' motivation but also play a key role in maintaining their active involvement in the project. The fact that network centrality (k-core) also plays a crucial role suggests that participants who are more integrated into the collaboration network are more likely to stay engaged, further emphasizing the value of fostering strong community connections within open-source projects. From a theoretical standpoint, this study contributes to the growing body of literature on open-source software development by offering detailed insights into the behavioral factors that influence long-term participation. By integrating k-core decomposition and SHAP analysis, this study provides a nuanced understanding of how network structure and PR management practices affect participant retention. These insights offer practical guidance for project maintainers, emphasizing the need to streamline PR handling and encourage participant integration into the project's core network. While this study provides valuable insights into the factors that influence participant engagement in GitHub projects, there are several limitations to consider. First, data collection limitations could have impacted the results. The study focused on a sample of GitHub repositories, and while the sample size was substantial, it may not be fully representative of the diversity across all GitHub projects. Additionally, participant behavior may vary depending on the type, size, and visibility of the project, leading to potential biases in the data. Second, there are limitations in generalizing the findings. The study is based on specific open-source projects within GitHub, which may not generalize to other collaborative environments or platforms. GitHub's unique features, such as the PR system and the community-driven nature of open-source contributions, may not directly apply to other contexts such as private repositories or non-software-related contributions. Third, while k-core centrality was utilized as a primary measure of network centrality in this study due to its strength in identifying cohesive substructures within networks, it provides only a partial view of a participant's role in the collaboration network. For instance, k-core does not capture the direct influence or connectivity strength of contributors, which metrics such as Degree Centrality, PageRank, or Betweenness Centrality can provide.